[Taiyz]

I use TokyoTosho to find my torrents, IsoHunt for batches, Azureus to download torrents and Windows Media Player with the Combined Community Codec Pack to play them. I use Media Player Classic for temporary videos, RealPlayer for temporary music, Quicktime for the .mov plugin because otherwise it's horrible and obtrusive, and Winamp for general music.

Otherwise, I'll use BleachExile for direct downloads when a subber I don't normally follow gets an episode out early, and either fourzerofour.us for direct downloads or Veoh for steams of shows I want to show other people (BE can also work in this category though.)

I use YouTube for finding MADs, although I typically will just add them as a favourite there, then copy and paste the video name into Google and watch it on Nico Nico Douga for the original quality.

Edit: Goddamn it, the board ate my edit. I had this follow-up about XviD and h264 but...
Anyway; I like XviD because it's light and my 360 can run it on a proper TV. h264 gets annoying with video lag; it's not a very refined codec. Definitely the quality points go to h264 however, if you can run it.