I'm loving using big, 16" x 20" canvas paper for painting. I splash colors, wait a bit to dry, and splash some more. I'm using acrylic paints with my brushes, my hand, fingers. It's a fun way to paint. I've discovered that a sheet of paper that size can then be cut into 30 Artist Trading Cards (2 1/2" x 3 1/2").
After the initial painting, I cut the paper into the cards. Then I add more paint. I use Sharpie paint pens (these are water-based) to write words and add extra lines and dots to the cards. These pens are great for adding a quick border to the card. On the back, I use a rubber stamp for my name, or just sign it with a pen.
I gave out most of these ATCs back in October when I was in Portland at Art & Soul. I have a few extra -- email me if you'd like to trade.