I am going to post on ATCs all week.What is an ATC? Oh, sorry, it is an Artist Trading Card. Did you ever trade cards as a kid? Baseball Cards, Football Cards, Marvel Comic Cards, Garbage Pail Kids? Same thing, but these are for artists.
Make a small (2.5″ x 3.5″) piece of art on sturdy cardboard.
Then what? You trade them.
Where and with who? swap-bot, ATCs for All, yahoo groups for ATCs, etc.
Here is what I have made recently:

Right now I am in an -athon (an ATC creating marathon) on ATCs for All.  I will keep posting what I make and some of my faves from others.