I watch video content from many different sources. While Netflix streaming on the Xbox covers my entertainment most of the time, occasionally I'll have media files (AVI, MKV, etc) that I'll throw on a thumb drive and watch on the PS3. This isn't much of a hassle, but every now and then a file won't be recognized (like the MKV file I tried to watch last night).
My frantic Googling led me to this software: http://www.ps3mediaserver.org/
Basically, you start the program, it finds the PS3 (or 360) on your network, and suddenly you have a window into your computer's file system appear on your PS3. It actually works with Mac as well (I'm a Mac guy). Just navigate to your videos (or audio, photos, etc) and click away.
I also use AppleTV for essentially the same thing (and I vastly prefer that for music and photos), but the AppleTV doesn't play all video formats. This software seems like a much more "no nonsense" solution for video (and it's free).