Depends on my mood. Sometimes, I don't want to listen to music when I want to concentrate, and other times it is essential. Sometimes, I can hear the music, and sometimes I tune it out when I'm concentrating :).

Bill Evans - Live at the Village Vanguard
Nick Drake - Pink Moon
Derek and the Dominoes - Live at the Fillmore
Richard Devinck - Going To California: A Classical Guitarist's Tribute To Led Zeppelin

Autocad & MicroStation as well. I also do a good bit of programming. I'm a bit odd that I have to have something very fast paced, like Linkin Park, to keep my energy up. It has to be loud! Classical puts me to sleep.

I also can think straight if I'm not working fast. I have a very short attention span and need to really keep going to concentrate and remember what I was trying to do.

i like to use the LOTR sound tracks. German Folk music does it also.