I've been learning about the Atmel AVR microprocessors recently and ordered a very nifty little demo board called the AVR Butterfly. I bought mine from Mouser for US$21.
The board is handy in that it has an LCD display, a clock, temperature sensor, noise maker, 5 way switch (kind of a pokey little rocker), and a place for a light dependant resistor. (It no longer ships with an LDR as I guess they contain lead).
It comes flashed with a very comprehensive demo program that fully demonstrates the capabilities of the CPU and supplied hardware. The source code is in C and has been ported to gcc.
I installed the avr-gcc tool chain with this installer and use the java AvrFlasher with a Keyspan USB serial adapter at 19200 baud. Note that I needed to set line endings to LF in AvrFlasher's serial settings for things to work. Until I tried that I was getting mysterious flash failed message with no clue about what was wrong.
This board is an absolute bargain for the price, and the display is a great feature, but aside from working with the naked chip, like my favourite the ATMega8, my vote overall goes to the Arduino board.