For me, I think working on systems and programming comes down to two different types of music. If I'm performing some system maintenance or deep system work or related programming, I find that techno/dance/trance helps... specifically soundtracks to some of my favorite movies that had techno in them are great for getting the draining mood effect that system programming can sometimes have on me. Miami Vice soundtrack has some great tracks that when listening keeps me feeling like I'm /solving a problem/ when I'm deep into the mix... Hackers, the movie soundtrack, is another good one that I like; Swordfish is another good one.
When it comes to creativity and problem solving at the development level, I find that like others here, either no music or classical music on low volume assists the concentration. Beethoven, Bach, and Mozart, etc. I truly find classical helpful... I read once that it actually stimulates the proper receptors in the brain that involve critical thinking, but I'm unable to find that link as a source. I stumbled upon classical years ago at random I think... I never liked it before then and I'm certain for some it can be an acquired taste.
I like Bach and other Baroque music for play during concentration tasks. Beethoven, Chopin, and the like are too dynamic and emotional. Can you imagine trying to concentrate to the fourth movement of the ninth symphony or the second of the Missa Solemnis? Not all classical music suits all moods.