Which external programmers work reliably with Arduino Mega? 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.
I have successfully used Arduino as ISP (not to be confused with Arduino ISP) on a Mega clone that has a funky FTDI-clone onboard, and would not let me upload bootloader through serial. This worked fine, and is cheap.