I remember enjoying the Z80
Some of the Renesas processors are very z80-like. Or perhaps 8080-like.
This includes the RL78/G13 that was recently the target of a contest with free dev boards available.
Actually, it was a bit depressing to discover; I sort of expect most chips available today to have either reached a certain degree of HLL-compatible elegance (like the AVR or MSP430 or ARM), or to have remained stubbornly "quirky" (like the 8-bit PICs.) I wasn't expecting an architecture to look mostly ... old.