I also prefer to work without music, but I use it to switch my brain into "action mode".

The music I tend to use for such mood-switching is usually energetic and sometimes aggressive (examples include action pieces from movies like Predator 2 or Matrix, various electro DJs, selected rap / hip-hop etc.) -- and I stay away from serious music (in my case its mostly Arvo Pärt, John Tavener and J.S. Bach).

Also, music is sometimes helpful for mentally isolating myself from coworkers, especially when they bug me with questions -- however, just putting the headphones on without music can do the trick. I read that Tim Ferris does that too.