I actually don't like Day[9]'s casting that much. His dailies are great, and so on, but I don't like his casting.

PsyStarcraft is great for diamond and lower zergs to learn some strategy, although he is quite crude. To say the least.

HDStarcraft can be amusing, but he is slowly dropping out of the scene as far as I can tell. He does work with IGN to do more professional stuff, but the channel is dying.

LagTV is funny, but definitely not a place to learn SC. Pretty crude at times as well. This is the most unique, in that they do only fan based games. Best known for when cheese fails.

Ahnaris is pretty good, but I don't have enough time to watch him that frequently due to the others I have listed.

Oh I forgot Husky, somehow. Husky is probably the best solo caster in terms of entertainment. His knowledge of the game mechanics is sometimes dodgey, and misses a lot of stuff in terms of drops. That said he is by far the most funny and energetic for casting.

Those are the only ones I can remember while sitting here at work.