AVR-PG1 is the most simple and inexpensive AVR programmer on the market. It works with the great free AVR programming software made by Claudio Lanconelli - the Pony Prog you can always look at the list of the supported devices on this link as it grows every month.

FEATURES

connects to PC via RS232 port (note it will not work with USB-RS232 converters!)
no need for external power supply as it takes the power supply from target board.
uses Atmel's 2x5 pin ICSP connector layout
dimensions 45x30 mm (1.7x1.2") + 20 cm (8") cable