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
(which, incidentally, had video hardware designed by the same team). Also, 256 colors were not seen in game consoles
until the Atari 7800
, and the SNES