http://www.cedarseed.com/air/atc.html
I signed up for a swap on a cool website called Swap-bot (http://www.swap-bot.com/) You can sign up for all different types of swaps, not just ATCs. People swap books, postcards, letters, stickers, scrapbooking materials, fabric, vintage items and a million other things!
I sent off my first ATCs to my two swap partners - one in Washington state and one in England. The theme was insects. The one pictured at the top of this post is one that didn't make the cut and get sent out, but I was still pretty happy with it.