This website has a list of anti-war songs, mostly pre-2001, and then makes this comment:

Less than five years after 9/11, the dearth of war-related songs from either the left or the right suggested that the fondest hopes of the Cheney-Rove crowd have been realized: We've normalized to being at war in perpetuity. Why sing about something that just is?

I've seen this complaint about a lack of current bands doing anti-war songs post-September 11th on a lot of lefty blogs as well. The thing is, i'm not sure that it's true. Without thinking too hard about it, you've got:

System of a Down - Boom!, among others
Green Day - an entire album, American Idiot
Sleater-Kinney - Combat Rock
Public Enemy - What Good is a Bomb?, among others
Dead Prez - Know Your Enemy
Saul Williams - Not In Our Name, among others
Trans Am - an entire album, Liberation

In addition you've had a couple of Rock Against Bush nu-punk compliations and i'm sure we could think of other examples. Is the problem that a lot of older people are remembering that songs like Merry Christmas (War Is Over) and Masters of War were actually on the radio back in the 60s and 70s, and they are wondering why the people on the radio today (Britany Spears and... my god, i don't even know who is on the radio) aren't coming out with political songs? They do know how commercialized music has become, right?

don't forget about those 2 Skinnee J's. i mean, this is a band that derailed its life's mission of having a good time, just to fight against the war. we all owe a great political and musical debt to the 2 Skinnee J's.

Newest Beastie's too