For something that's free to download KM Player is the best media player I have found so far.
These are the main reasons why:
1) It has no problem playing (and re-playing) Flash Video Files unlike VLC Player, Windows Media Player and many other media players
2) It allows you to (easily) take snapshots of videos
3) It plays virtually EVERY type of media format that exists. I think the only video format it can't play are Realplayer video files but I could be wrong
4) You can make the viewing screen as big or as small as you want
5) When playing videos you can make the picture: darker, lighter, sharper, rotate it, slow it down, speed it up, reverse it, etc, etc.