1) The Bible says homosexuals will go to Hell

Romans 3:23 says For all have sinned, and come short of the glory of God.  This means that all human beings are guilty of sin, so no special group (e.g., homosexuals) are doomed to go to Hell.  Anyone can make it to Heaven if they accept Christ as their personal Savior.

2) Sodom and Gomorrah were destroyed for being gay

The act mentioned in Genesis 19 before Sodom and Gomorrah were destroyed was attempted gang rape.  The two angels mentioned in the passage were strangers to the city and the people of Sodom did not receive them with welcome.

Behold, this was the iniquity of thy sister Sodom, pride, fulness of bread, and abundance of idleness was in her and in her daughters, neither did she strengthen the hand of the poor and needy.
(Ezekiel 16:48-50)

It's not homosexuality that's the issue here, but inhospitality.

3) Leviticus 18:22 and 20:13 say that homosexuality is an abomination

Thou shalt not lie with mankind, as with womankind: it is abomination. (Lev 18:22)

If a man also lie with mankind, as he lieth with a woman, both of them have committed an abomination: they shall surely be put to death; their blood shall be upon them. (Lev 20:13)

The word "abomination" used in these verses was translated from the Hebrew word to'ebah, which means "a disgusting thing."  However, given the context that it was used, the word always referred to an act of idolatry.  Leviticus 18:21, the verse right before "thou shalt not lie with mankind," states:

And thou shalt not let any of thy seed pass through the fire to Molech, neither shalt thou profane the name of thy God: I am the Lord.

The subsequent verse 22 is actually grouped together with this one.  Here are a few other places in the Bible that use the word to'ebah in the context of idolatry:

There shall be no whore of the daughters of Israel, nor a sodomite of the sons of Israel.
Thou shalt not bring the hire of a whore, or the price of a dog, into the house of the Lord thy God for any vow: for even both these are abomination unto the Lord thy God.
(Deuteronomy 23:17-18)
And there were also sodomites in the land: and they did according to all the abominations of the nations which the Lord cast out before the children of Israel.
(1 Kings 14:24)

Here are some other verses, to put the word sodomite in context:

And he took away the sodomites out of the land, and removed all the idols that his fathers had made.
(1 Kings 15:12)
And the remnant of the sodomites, which remained in the days of his father Asa, he took out of the land.
(1 Kings 22:46)
And he brake down the houses of the sodomites, that were by the house of the Lord, where the women wove hangings for the grove.
(2 Kings 23:7)

The use of the word "sodomite" here was translated from the Hebrew word quadesh, which, in this context, refers to a temple prostitute.

Note: the Talmund equated the acts of these "sodomites" with the prohibition in Leviticus 18:22 and 20:13

4) Deuteronomy 22:5 says that cross dressing is an abomination, and therefore transgenderism and transvestitism is a sin

The woman shall not wear that which pertaineth unto a man, neither shall a man put on a woman's garment: for all that do so are abomination unto the Lord thy God.

Again, the word for "abomination" here was to'ebah, which is relevant to idolatry.  The act being mentioned here is a reference to what the pagan cultures did in their cultic rituals.  They often anally injected themselves with drugs, which induced such a high sense of ecstasy that they felt as though they could do anything.  Many times, this resulted in cross-dressing and self-mutilation among them.

5) Romans 1:26 [specifically] condemns lesbian behavior

For this cause God gave them up unto vile affections: for even their women did change the natural use into that which is against nature:

The phrase "against nature" referred to non-procreative sex or or a reversal of roles in sex, not necessarily lesbian sex.  What these women were doing was having sex with men in in such a manner that would not produce children, which included anal sex, oral sex, and occasionally using a dildo to engage in anal sex with men. In this case, the prohibition here appears to be against all forms of "unnatural" sex, especially the ones preformed in a cult.

However,

The interesting fact is that the Bible has never condemned non-procreative sex within the confines of a marriage. Therefore, the prohibition in this passage must not be referring to the "unnatural" sex acts per se, but the fact that these people were abusing their sexual relations in the first place.

6) Romans 1:27 condemns all male homosexuality

And likewise also the men, leaving the natural use of the woman, burned in their lust one toward another; men with men working that which is unseemly, and receiving in themselves that recompence of their error which was meet.

This act is obviously a homosexual one.  However, given that this in the context of idolatry, it does not condemn a committed relationship between two men, but instead, ritual temple sex.

7) 1 Corinthians 6:9 says homosexuals do not enter the kingdom of God

Know ye not that the unrighteous shall not inherit the kingdom of God? Be not deceived: neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind,

Some people incorrectly interpret the word "effeminate" as "a male who acts like a woman."  However, the Greek word malakoi actually referred to someone who is morally soft.

The biggest controversy is over the word arsenokoitai, which translates to "abusers of themselves with mankind" here.  Most modern Greek Lexicons will translate this word as "one who lies with a male as with a female, sodomite, homosexual," but this is a faulty translation.  The word originated in Koine Greek, which is far different from modern Greek, and its meaning has also changed over time.  According to a couple of ancient texts which use the word arsenokoitai, it does not refer to homosexuality in general:

the Apology of Aristides, part VIII:

"The Greeks, then, because they are more subtle than the Barbarians, have gone further astray than the Barbarians; inasmuch as they have introduced many fictitious gods... some were kidnapped by men, and some, indeed, were lamented and deplored by men. And some, they say, went down to Sheol, and some were grievously wounded, and some transformed themselves into the likeness of animals to seduce the race of mortal women, and some polluted themselves by lying with males"

The context of arsenokoitai in this excerpt referred to the Greek gods forcing themselves on mortal men, not "homosexuality."

the Refutation of All Heresies, by Hippolytus:

Naas, however, has committed sin, for he went in unto Eve, deceiving her, and debauched her; and (such an act as) this is a violation of law. He, however, likewise went in unto Adam, and had unnatural intercourse with him; and this is itself also a piece of turpitude, whence have arisen adultery and sodomy.

In this context, the act here was referring to male rape, as Naas did not seek to consent with Adam in his sleep.*

8) "God made Adam and Eve, not Adam and Steve!"

This sounds like a thought-terminating cliche to me.  It's a common cop-out of any argument on homosexuality, which basically states "God made the first two people heterosexual; therefore all people were meant to be heterosexual."  This is not true.  One might argue Jesus' statement in Matthew 19:4-6

And he answered and said unto them, Have ye not read, that he which made them at the beginning made them male and female,
And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh?
Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder.

The context here was divorce.  He was saying that once two people are united, then no law of man should de-unite them.

Jesus also mentions an exception to the one-man-one-woman rule in verse 11-12

But he said unto them, All men cannot receive this saying, save they to whom it is given.
For there are some eunuchs, which were so born from their mother's womb: and there are some eunuchs, which were made eunuchs of men: and there be eunuchs, which have made themselves eunuchs for the kingdom of heaven's sake. He that is able to receive it, let him receive it.

The most common understanding of a eunuch today is a man who has been castrated so he could not take pleasure in a woman.  However, in the ancient times, people were aware of some men who simply were not attracted to women, and classified them also as "eunuchs."  These are the people Jesus mentions in verse 12 who are "born so from their mother's womb."

An interesting quote from Clement of Alexandria states "A true eunuch is not one who is unable, but one who is unwilling, to indulge in pleasure" [with a woman]

9) If we discount the verses following Leviticus 18:21 about Molech because they were idolatrous, then bestiality must be okay too

what about the prohibition following that one, about having sex with animals? Can we say that no such prohibition existed if you wanted to have sexual relations with an animal, as long as it wasn't having to do with a religious rite?

Yet perversions of all kinds are more and more accepted today. In the 1990s on a college campus, a group mocked the campus sponsored GLAD (Gay and Lesbian Awareness Days) week by promoting their own cause: BAD (Bestiality Awareness Days). Though in bad taste, they made a valid point: On what basis do we say that one is wrong and unnatural and another is not? If there is no God, then everything is permissible; it is all a matter of opinion and preference and nothing else.

this may seem like a valid claim, but there's one slight issue here:

Thou shalt not lie with mankind, as with womankind: it is abomination.

Neither shalt thou lie with any beast to defile thyself therewith: neither shall any woman stand before a beast to lie down thereto: it is confusion.

tow'ebah: properly something disgusting (morally), that is, an abhorrence; especially idolatry or concretely an idol ("abomination")

te'bel: mixture, that is, unnatural bestiality ("confusion")

The Bible actually states the difference between the act of two men engaged in anal sex and bestiality.  The former is in the context of idolatry, meaning it was forbidden as a cultic practice.  The word "abomination" specifies that the forbidden aspect of the "homosexuality" was idolatry.  The word "confusion" on the other hand specifies that the nature of the bestiality act was an unnatural mixture.  It was forbidden because it was unclean in itself, not because it was connected to idolatry.  If the two were equally vile for the same reasons, then the same word te'bel would have been used for both.