If you want to make 2D vector art and can't afford Illustrator:
(See SpriteAttack's awesome blogspot: 2dgameartforprogrammers.blogspot for some excellent game art tutorials using inkscape.)
Also, you can render 3d objects to create 2D sprites, too. Here are some free tools in order of increasing learning curve:
Daz Studio from daz3d.com uses poser-compatible content. Tons of free and paid content at various sites.
Sketchup Content at the google 3d warehouse.
There are many more tools. So much depends on what you are trying to do--that is, what kind of game and what style of game art.