Your homophobic uncle might not be to happy about it, but surprise! Gay marriage is legal in New York. And since New York is the center of the universe as far as me and the rest of the other arrogant New Yorkers are concerned, it's only a matter of time before other states follow suit. Sorry, Uncle Jim, the gays are going to get hitched and live much more fashionable lives than you (well, not the lesbians).
But now that you're going to be invited to more gay weddings, you have to walk the fine line between going too far to the gay pride left, and going too far to the conservative right.
You don't want to be bush league and get them a bunch of stuff meant for straight people (His and Hers towels, contraceptives, etc), but you also don't want to get them a bunch of rainbow candles or weird sex toys.
These Gay Wedding Cards ($3, La Familia Green) are perfect. They acknowledge the fact two gay people are getting married without being over-the-top. An example of an over-the-top wedding card would probably be covered in glitter, decked out in rainbows, and when you open it, it would sing "Do You Believe" by Cher. STOP IT, YOU'RE TRYING TOO HARD.