The C64 had a 6510 (later 8510) that is different from the 6502 pretty much only in that it had 8 general purpose IO lines, some of which were used for bank switching (to map the ROMs in and out of memory over the RAM), and some for the tape connector at least. I don't remember what all 8 lines were used for.
They're pin-compatible enough that in some devices you can swap them around and get things to work (e.g. putting a 6510 in a 1541 has a decent chance of working unless the GPIO pin register clobbers something important in the 1541 memory map; with the reverse you'll at least have problems, though a 6502 in a C64 might work if you only run things like cartridges and/or put the right voltage on the right pins to map the ROMs into place).
Also, the Amiga 500 keyboard had a 6502 compatible CPU with built in PROM and RAM as well (MOS 6570).
http://en.wikipedia.org/wiki/Commodore_1541 indicates that my memory is correct, but http://en.wikipedia.org/wiki/Commodore_64 says that the chip on the C64 itself is a bit different, though.