Now that systems are so powerful, there doesn't seem to be anything like the fun challenge of trying to get the most out of some 8-bit micro and with less than 64kb memory. Is there something (that isn't an emulator) which can provide a similar experience?
EdSim51 is a free 8051 simulator. The 8051 is a great microcontroller.
The simulator has a virtual keypad and LCD display.
The BASIC Stamps are good too.
http://www.radioshack.com/product/index.jsp?productId=2117994 http://www.parallax.com/tabid/295/Default.aspx
Check out the http://www.arduino.cc/. There are lots of project ideas based on it if you Google for it.
I always wanted to try out the BASIC Stamp modules but have never quite found the time.
Many of the kits available from Adafruit Industries are based on 8-bit AVR microcontrollers, excellent for electronics and programming tinkering.
The Arduino is a great starter CPU. I've used boarduinos to program other AVR microprocessors as well. BASIC stamps are easy to use, but I think the price for what you get is poor.
Eclipse with the AVR plugins makes a great Arduino development environment (what I use right now).
There are also some interesting kits mentioned in response to the What’s the best way to learn how to build circuits question.
If you just want fun out-of-box programming, have a look at a Tandy TRS-80 Model 100. It boots up instantly, runs on 4 AA batteries, has a very sharp LCD display and built in BASIC. The keyboard is fantastic! A working model can be as low as $75 (See the Club 100 Store).
I like the 8-bit AVR microcontrollers, but sometimes it is nice to have a big LCD, an interpreted language and a keyboard. Have fun.