Ah, there are so many, here's a list of some of my favorites, in no particular order. (The "Creative Loafing" top 10 at the top of the thread seem to include only mainstream songs, which does not necessarily make them the best options.)

Wartime President Song - Ariel
Price Of Oil - Billy Bragg
My Uncle Is A Terrorist - Bruce Lesnick
He Swapped The Bottle For The Bible - The Bushwackers
Dangerous Times - Chuck Brodsky
Talkin' Al Kida Blues - Dan Bern
Hey There Mr President - Dave King
12 Days of Bushmas - Dave Lippman
Texas Air National Guard - David Hershey-Webb
I Have Seen The Enemy - David Rovics
Bomb Ourselves - David Rovics
Operation Iraqi Liberation - David Rovics
September 11 The Day The Universe Changed - Ethan Daniel Davidson
I'm George W - George Mann
Its Hard To Put Food On Your Family - George Mann
King George III - Hugh Blumenfeld
Go Home Terrorist - Jerry Isham
Yellow Stain From Texas - Joe Befumo
Hail To The Chief - John McCutcheon
International Cowboy - John Warner
You'd Better Keep An Eye On Him - Jonathan Byrd
Homeland Security Blues - Ken Ficara
Freedom Avenue - Michael Brewer
Dont Be Afraid of the Neo Cons - Norman Blake
Somewhere Down The Line - Old Number 8
My Hero Mr President - Paula Cole
Cowboy (Ode To Dubya)- Peggy Watson
Chickenhawk Blues - Peter Dyer
Dear Mr President - Pink
Houston Texas DC - Scott Morrison
You Aint A Cowboy - Stephan Smith
Bushwacked - Steve Brooks
The W Song - Ted Blackwell
George W Told The Nation - Tom Paxton
Cowboy President - Yikes McGee
The Freedom Wall - Freebo
When You're Back On Your Ranch In Texas - Tom Pacheco