ladyada has released the Fuzebox, an open-source 8-bit game console. Features:

Full 256 simultaneous output colors, 240×224 pixel resolution
Tile & sprite support
Two player ports, either with Super Nintendo or classic Nintendo controllers (although the kit comes with SNES)
NTSC RCA composite and S-video out (PAL not supported at this time )
4 channel PCM output mono [...]