By rotating, positioning and dropping a predetermined sequence of pieces, the Tetris Printer Algorithm (video) exploits the mechanics of Tetris to generate arbitrary bitmap images.
VectorMagic is a new site that uses technology from the Stanford University Artificial Intelligence Laboratory to transform your bitmap images into vector art that can be scaled without becoming blurry of pixelated. Here's the first image I submitted, before and after.
BitFontMaker - Create, edit, and save your own truetype pixel font via this web app.
Apple ][ font : The ultimate in retro bitmap. It even includes the mouse text characters so you can "draw" Apple ][-style windows. Neat.