"The Biological Equivalent of Apple Pie"
It's a fantastic article, and gives plenty of examples of gay animals. One warning, though: the article is very explicit - think carefully before showing it to your mother.
I want to print a copy and have it available at a moment's notice, to show to all those people who constantly say homosexuality is "against nature" as a way to justify discrimination against gay people. But what nature are they talking about? Obviously not the one on Planet Earth.