My favorite has to be John Bain (Totalhalibut). Mainly because he does so much variate content on all kinds of games.
Crota is one of the best commentators on SC2 and WC3 TFT - Which isn't something you see a lot of these days.
Day9 is awesome if you want to check a lot of strategy and "noob" friendly reviews of games done by the pros.
Jesse Cox has an amazing humour and he takes gaming to a whole new level with his interesting and funny videos on various games.
The guys from Machinima Respawn are also extremely fun to watch, specially their game battles where their teamwork really shines, although Seananners is the guy with the most popularity on various games.
The yogscast is a little... Too much for me. The highpitch noises from Simon gets extremely frustrating after the first 5. Lewis is alright though.