From a beginner's view, one 8-bit MCU is pretty much the same every other. Since you used a BASIC Stamp, guessing you can program in BASIC. There are plenty of compilers, many free, for most brands. Starting out, you won't need to worry about memory size or processing speed, all have more then enough to flash a few LEDs...
Considering your numerous, a similar style posts. I would suggest MicroChip PIC. There is a ton of tutorials and complete project sites on the web to learn from. There are build your own programmers for $10 or less (depends on how much junk you collect...).
Unless you have some specific project goals, the chip specifics really won't make a huge difference at first.