I've tried tons of alternatives including all of the ones mentioned here (in the comments area) and i find these are the best, in order of importance, and the reasons why:
1. Gom Player
Why?: It seems these guys decided to look and steal the best of what makes the other players good and incorporate it into a very smart, clean interface. It can play some partial files but can't play some things like Vobs, and Bin files
Download: http://www.gomplayer.com/download.html
2. Vlc Player
Why?: This is the granddaddy that can play ANY video file out there. It's user interface is GAWD-AWFUL (quite possibly the most annoying and developer abused tool when it comes to user interface ever). It is solely because it can play ANY movie file including ANY partially downloaded video file that makes it a very important part of video players. Besides that i have only bad things to say about this program.
Download: http://www.videolan.org/vlc/
3. Media Player Classic
Why?: This one was put together by a hacker team who was fed up with Microsoft and their half-arsed work on Windows Media Player and took the v6.0 Media Player and spruced it up BIG TIME. It has a lot of features and can play some partial files well,
Download: http://www.afterdawn.com/software/video_software/video_players/media_player_classic.cfm
For me i use ALL 3 of these ones together since each can do something the other cant. But Gom is the closest to being perfect. For you i recommend you get Gom Player and depending if you are a big p2p downloader i would also recommend u get Vlc Player too (to play partial movie downloads -- this program is incredible at that).
I also recommend you download and install the K-Lite Codec Pack..this will give you all the video codecs that you need to play ANY movies/videos that you come across without concern for cases like video runs but no audio, or vise-versa...
K-Lite Codec Pack Download Page: http://www.codecguide.com/download_kl.htm