Gamespy has a post with the official, tiered, in-game rankings for each song and instrument.]
If you're anything like us, you've been gearing up for Rock Band 2 by poring through the track list and carefully studying YouTube performance clips of the songs to gain an edge in your own virtual rocking. But staring at grainy video is only so useful for determining which songs are really going to put blisters on your fingers (and uh, vocal chords). Luckily, IGN has come through with a set of comprehensive difficulty rankings, for all 84 RB2 songs, ranked by individual instrument and as a full band.
We're not entirely sure where IGN's rankings are coming from -- we can only assume they're based on the difficulty rankings provided by Harmonix (don't ask us how ties are broken). That said, based on our extensive knowledge of all things rock, it seems pretty accurate -- any group that can pass Judas Priest's Painkiller on Expert without turning on No Fail Mode should just start a real band already.