The custom GPU inside the Atari 400/800, and its video console incarnation, the Atari 5200.
For a home computer, the ANTIC's capabilities were very much ahead of its time. The ANTIC was implemented as a DMA-based (or "display list") coprocessor, taking instructions from the CPU and processing them itself. This made creating impressive demos and display hacks easy.
The other half of the ANTIC system was it's TV output chip, the TIA. The first revision, the CTIA, could put up to 128 colors on-screen at once; the
1981 upgrade, GTIA, increased this to 256, making the ANTIC system the best video subsystem in home computers until the debut of the
Amiga in
1985 (which, incidentally, had video hardware designed by the same team). Also, 256 colors were not seen in game
consoles until the
Atari 7800 in
1986, and the
SNES in
1990.