If you want to play with real code on real hardware, then the Dallas DS2250 is a very simple way to start - you get everything you need except a crystal and a serial interface on the DS2250. There are other chips with bootstrap loaders, but never with XRAM as well. The 2250 has all its port pins free for external hardware too.

The only drawback is that the 2250 is only an 8031, so you don't have the power and usefulness of timer 2.

They cost about $30.00

If you want to build your own stuff from scratch, the the 89C52RX2 from Philips is very good indeed, with a free download utility available from their website. Atmel do another series of ISP parts, but programming is more complicated than for the Philips or Dallas parts.

Steve
Steve