I feel it's my duty to throw in a plug for the Motorola 68HC08 series here. We have used them on our custom circuit this year and last year. They're comparable to PICs in processing power. The hardware necessary to program them is extremely simple (and cheap) to build and the software (assembler, simulator, in circuit debugger, in circuit simulator, and code download program) is free. Also, Metrowerks has a whole suite of programs (including a C compiler and IDE) available for free as well. (Check out
this link and scroll to the bottom for more info on that).
If you're interested in the HC08 stuff, ask away with more questions and we should (hopefully) be able to answer them for you. They are fun, easy devices to work with and we've had nothing but success with them!