When looking for alternate external programmers (ISPs), I am noticing that many are not Arduino Mega 2560 compatible (e.g. Pocket AVR Programmer, USBtinyISP).

I am looking for a reliable external programmer for the Arduino Mega that is compatible with the Arduino IDE. What are my options? Currently I have been struggling with the retired ArduinoISP programmer, which doesn't look like its going to work. Does anyone have proven experience with a given programmer and a Mega?

The suggested AVR-mkII doesn't seem to be available anymore either.