VLC is the awesome-est media player which plays almost all the video formats out there. It is my default media player. Sadly it cannot be my only media player, since it has partial support for Real Media files (.rm or .rmvb). This means that some Real media files play fine, some have seeking problems and some just do not play at all.
One solution for this problem is to install the Real Alternative codec pack. It ships in two forms:
Real Alternative Lite: Just the codec files.
Real Alternative: The codec plus an old version of Media Player Classic to play the files.
I like to have as few files around as possible. So, I prefer to install Real Alternative Lite and use Windows Media Player to play the files.