Anything I rate 4 stars or higher in my library I usually play while working. These tend to be songs I’ve listened to a lot so I don’t think about them much while they are playing, a good thing when trying to focus (for this reason I avoid playing Last.fm radio during work… most of the time).

That being said I play BoA (Korean pop), Blutengel (German electronic/dance), Eisbrecher (German industrial) and Velcra (Finnish industrial) the most during that time.

Most of the time i shuffle my music library. I skip tracks that distracts me easyly with gnome do. If i really need to concentrate, i prefer beethoven or dubstep.fm podcasts. In dubstep.fm podcasts, especially there is a dj named jungle visionary. I would recommend him.

Gold Panda, Four Tet, Baths, Toro y Moi, Caribou, Pantha du Prince - http://www.rhapsody.com/myrhapsody/playlists?playlistid=mp.1...

I think you would like Bonobo. He released a really good album this year. And Flying Lotus as well.

Classical Beethoven and Mozart and Pachelbel and Vivaldi

Or typical heavy metal.

Instrumental. Cinemix on iTunes. Favorite is Hanz Zimmer's soundtracks.

any specific?

Led Zeppelin Indian Classical (Raag Deshkaar) Instrumental

Deadmau5, almost exclusively, or Groovesalad from soma.fm.

Tech house, mostly. Or warp/rephlex/mu stuff.

Lady Gaga.

...whatever local radio plays.

You don't have a preference? Nothing stands out as better than the other? Can't even give us a genre?