We frequently use breadboard adapters for all the Atmega microcontrollers we're using and all adapters have 6-pin ISP headers. Unfortunately our programmer (AVRISP mkII) expects the target to be powered by an external source. To avoid needing a power supply when tinkering we decided to mod the programmer to provide 5V power via the USB port.
The mod simply consists of one soldered wire; from the USB pin 1 (VCC) to the backside of the pcb; pin 2 on the 6-pin ISP header. The wire runs via a switch that allows us to use the programmer with already powered boards as well.
It could be considered a bit crude but it gets the job done for prototyping. Future improvements could be adding 3.3V power and proper regulators and perhaps a polyfuse of it's own.
