[wk_end]

Some SNES games offloaded varying degrees of computation to on-cart chips, but I don't believe any NES games did. There was a Hellraiser game in development for the NES that was supposed to ship as a Z80-powered "super cartridge" but it was canceled.

[djmips]

The only thing I could dig up was the Famicom Network System which was a cart released in 1988 which had a 65C02 on board. So not a game but it was a co-processor that was available on a 'NES' cart back in the day...