If you're wanting something simple (ie - 8 bit), there are microcontrollers out there based on 6502 and Z80 cores (maybe even 680x - but since Motorola is still around, maybe not). Many of these controllers have a ton of on-board peripheral ports, and a lot of RAM - but still bring out the address and data lines for expansion purposes. In many cases, they can be programmed using C - some also have an on-board BASIC interpreter (you essentially hook up a serial terming, boot, then start coding - storage is handled by flash or similar). All of them, though (just like the ATMega line for the Arduino) still support assembler and can handle what you want to do.