Any of the non-well known Queen songs:
Queen - Tenement Funster
Queen - Long Away
Queen - Death On Two Legs (Dedicated to...)
Man, I wish there was Queen Extravaganza 03 pack.
Although not DLC, I never expected to see Spacehog in Guitar Hero or Rock Band, but I guess that really isn't that surprising considering In The Meantime was a pretty popular song in the US. Would've been nice if they gotten some of their other songs too.