We recommend the USBtinyISP for burning the Arduino bootloader onto chips and for working with our AVR target boards. It can also be used to program our other AVR-based kits including Peggy 2 and Meggy Jr RGB.
The USBtinyISP is an open source kit that includes both 6-pin and 10-pin ISP programming interfaces. It can also optionally provide up to 100 mA of 5V power from USB to your target board. It works on Mac, Windows, and Linux. For more information, you can read the Evil Mad Scientist review of this kit here.