Two youtube commentators that I've thoroughly enjoyed listening too:
Senanners:
[video=youtube;83paMALiJFE]http://www.youtube.com/watch?v=83paMALiJFE[/video]
This guy almost never talks about video games. Instead, he talks a lot about what's going on in his life, how he feels about certain things, etc. I've never been much into Call of Duty, but Seannanners is very skilled at video games in general (recently, he's played nothing but Trouble in Terrorist Town), he's fun to watch, and enjoyable to listen too.
On the other hand,
ThePikaWu:
[video=youtube;5AzTb-DwSI0]http://www.youtube.com/watch?v=5AzTb-DwSI0[/video]
This guy does nothing but talk about his thought process, what he's doing, etc. Maybe it's because I'm so fascinated with competitive Pokemon play, but I love his videos. I think he has a good voice, and he talks in a way I can understand.
As far as live streams go,
TheOddOne is my go to guy. He constantly talks about what he's doing (he streams League of Legends), and he's super hilarious to boot.
[video=youtube;gvvcGe8Rjd8]http://www.youtube.com/watch?feature=player_embedded&v=gvvcGe8Rjd8#![/video]