This site has templates and an envelope template for ATC's if you are interested.
zine art or clipart
If you put Artist Trading cards in a search engine such as google you will come up with all sorts of information on these little works of art.
Oh another good source of information and some pictures of other's ATCs you can look at UKscrappers You must register with them and it is free. They have lots of information on lots of card making, scrappbooking and all sorts of paper crafting things.