I absolutely love Pandoc, I use it in my Makefile based static site generator. Pandoc is probably one of the most valuable pieces of open source tooling next to ffmpeg and imagemagick.
Pandoc for text, ffmpeg for audio/video and imagemagick for images?
I've used pandoc for pdf generation and ffmpeg for some audio recording/encoding/playback. I can't imagine what I would use imagemagick by itself for though (that I wouldn't use some common image processing application for). What do you use imagemagick to do?
