Just in case you haven't discovered it already, The Hype Machine is a great source for discovering new music. Apparently, it's a great place to revisit last year's music too.
They've compiled three Best Of 2008 lists of music to browse: 50 Songs, 50 Albums and 50 Artists. The 50 Albums list is really impressive since it includes streaming versions of all 50 albums in their entirety. As I type this, I'm listening to a band called Ra Ra Riot, and I'm really digging it. Their album The Rhumb Line is listed as the 43rd best of 2008.
Check it out HERE!