Whats the best free video player that will play .flv files on my PC?
VLC is definitely the way to go on this one. It will play almost anything you throw at it.
It has better support for Vista over the older version which has not been updated for over a year. It is freeware, open source, very snappy and light on resources.
CCCP includes all codecs necessary to play FLV files (as well as most popular formats), and also comes with Media Player Classic, which is my favorite player.
VLC's a great open source media player, but for Windows I prefer the KMPlayer's GUI, customization features and overall ease of use than VLC.
Like VLC, it can play almost anything you throw at it (including FLV files).
The KMPlayer in Wikipedia: http://en.wikipedia.org/wiki/K-Multimedia_Player
Note: KMPlayer is a Windows software and is freeware, but not open source.
Besides the previously mentioned really good players (like VLC media player which does work on very much platforms, and supports very much formats, or Media Player Classic Home Cinema, which also has 64 bit support), I can also suggest BS.Player (with e.g. Phoenix skin or Mgc3WMP skin, which are very nice).
This player also supports very-very many formats, and its subtitle correction and subtitle appearance customization options are very handy too, which is very important to me when watching films in other languages - in very many players, subtitle appearance customization is too complicated or oversimplified (I know VLC also has this capability, but I think it's a bit over-elaborated...).
It works only on Windows platforms (no Linux or Mac support) for the time being though (Windows 98/ME/2000/XP/Vista/Windows 7), but for Windows it's a really useful media player.