CCCP ftw. I use it too, except for one file type. Possibly mkv, if not, avi. It skipped about and the audio lagged on full HD videos, but another one fixed it (haven't got it on this computer yet, so can't find name atm).
I use VLC media player. The user interface is quite easy. The ability to quickly add directory makes it a really fine software. I can even add subtitles to the video. In my opinion, the best feature is the capturing of screen shots.
I use itunes simply because i was given an ipod for crimbo a few years back. installed itunes to add music to it and just haven't bothered changing it lol.