We took the business-card-sized AVR target board from Evil Mad Scientist Laboratories and added a few components to make an AVR dev board that has only the bare minimums!
Comes unassembled with:
We suggest using this board in conjunction with a USBtinyISP programmer (not included), and having the programmer provide USB power to the board. Of course, any programmer can be used, just make sure that you also power the target board somehow.
To get you started, here is a 'hello world' zip file. It contains a C program, compiled .hex file and Makefile for a blinking LED connected to pin PB5. Wire up the board as shown here (don't forget the 3 jumper wires up top, they are essential!) Then install WinAVR or equivalent and run make program in the uncompressed folder to compile and burn the example.
Can easily be turned into a 'Minimal Arduino', simply follow the instructions from TodBot (You'll need a programmer like a USBtinyISP or similar to burn the bootloader onto it)