BitTorrent clients

• µTorrent Micro-Sized Yet Feature Filled. Recommended
• Original BitTorrent Client Written by Bram Cohen, inventor of the BitTorrent concept.
• Azureus A popular Java client with automation features.

Media Players

• VLC Media Player Plays all kinds of video files (except mealmedia) with no need to install any codecs. A good choice if codecs confuse you.
• Winamp Plays all kinds of AVI and MPEG files provided you have the proper codecs installed.

Codecs

• DivX Codec The commercial DivX codec. There is a free version that shows a watermark on screen for a few seconds.
• ffdshow XviD-DivX filter This filter will set you up for playing XviD & all kinds of DivX files. If in doubt, just install this one, and you should be good to go for most files.
• AC3 filter Open source AC3 playback filters.
• Ogg Vorbis filter For those rare movie files that use Ogg audio.
• Real Alternative This is a codec for playing RealMedia files. (.rm .ra .ram) It works for all but the very oldest files.
• Quicktime Alternative This is a codec for playing QuickTime files. (.qt)

Other tools

• GSpot Gives you detailed mediafile info to help you track down any codec issue that may be preventing playback.
• Quick sfv If your download includes an .sfv file, run it using quickSFV to check the integrity of your downloaded files.