[Update for Arduino 1.6+, editing these files manually is not needed!, see 1.6+ instructions below!]

We think Pololu's USB AVR programmer is a pretty nice cost effective device for uploading code to AVR microcontrollers. (Not that we're biased or anything :) )

Many might not be aware that you can use the programmer with the Arduino IDE to upload Arduino sketches to "raw" (ie, non-Arduino) AVR chips. If you have a developer board with a 6-pin ICSP connector, or an AVR on a breadboard with an ISP adapter, it's fairly easy to use Pololu's programmer in conjunction with the Arduino IDE. Even if you are using an Arduino board, using a programmer has advantages over relying on the Arduino's built-in bootloader to upload code. Some bootloaders don't handle resets well, and can be picky about accepting accept new sketches. Also, the Arduino bootloader consumes space on the chip, so if you have a large sketch, you can reclaim some of that space by eliminating the bootloader and letting the programmer handle that function.
 

How to enable the Pololu USB AVR Programmer in the Arduino IDE