VLC - Pros: Great compatibility, no external codecs.
Cons: In most cases, newer encodes seem to break. If at all, run. And if it does, it's very laggy. Also, it uses a fuckton of memory being idle.
Suggestion:
Media Player Classic, and CCCP codec pack. Although, you don't necessarily need all the codecs, you might as well.
Zoom Player is good as well, but it'll be a bitch to some newer H.264 encodes and especially the 720p versions.