I'd highly recommend looking into Picaxe Microcontrollers. They are very similar to the basic stamps in programming and capabilities, but even have some capabilities that the stamps do not (like built in ADC and interrupts). Oh, they they start at like $3 and go all the way up to $8. The biggest downside I've run into is program memory, but I've heard they are working on that and for MOST uses I've come up with, it's been just fine.
