There are a couple of places where you'll find 2D artists (pixel artists). Check out
Pixelation and
Pixel Joint. They have galleries of their work there as well as contact details.
You'll probably find that many of the artists who will work for free are just beginners or high school kids, but it's worth a try.
I've been looking for artists to help out with a few game projects that we've been working on at Underground Arcade for a couple of years, but still have had no luck yet. Lots of people offer to help, or boast about what they can do, but in the end no one ever ends up doing any actual work. I think you'll have trouble finding anyone comitted enough to stick to a free project, especially if no one even has any idea what kind of game it is you're making in the first place.
Still, if you want to make some contacts I hope something comes out of it. Just don't be disappointed if those people disappear when the time comes to ask a favour of them.
