The 16-bit version of the venerable 6502. Laid out entirely by hand by William Mensch (and with a few hardware bugs as a result - MVN takes 3 cycles longer per byte than it should), the 65816 has 3 registers, a 24 bit address space, and no waiting :-)
Used in the Apple IIGS and the Super Nintendo. Many SNES games had slowdown because only former C64 and Apple II coders knew how to make it sing.