I know, sounds dumb, but bear with me a sec.
People here have posted links to tons of high-level replays with commentary. (Thanks.) They're awesome fun, and I can learn a little.
But since I'm a low-level player, it's a lot like watching Iron Chef: experts way above my current skill/understanding level duke it out, while expert commentators point out strategy errors so subtle that I often don't even understand why they're errors.
Are there commentary replays of low-to-mid level matches?
Tutorials like SC2 Noob School and Shokz are great, but they're not the same as watching a real match. And while it wouldn't be as sexy a gig for the commentators, it'd be a great teaching tool: watching 1,000 things go wrong, and having an expert point out which are most common, and which are most important to fix.
Best Answer
TotalBiscuit has a series called I Suck at Starcraft where he comments on his own noob games, focusing on what mistakes were made and how to improve.
The series starts out very basic, explaining economy, supply, teching, and the uses of some individual units. It should be understandable even for someone brand-new to SC2. The downside to this is that it may be too basic for many players. However, over the course of about 15 videos, he moves into (somewhat) more advanced concepts.