1. Tangerine Dream
2. Pink Floyd (early stuff, Ummagumma e.g. works well, but when thinking hard even Dark Side can get you side tracked)
3. Beethoven/Mozart
Nice range there ;-)
I agree words get in the way, but it depends what you're doing. If you're looking over stats or not doing anything too intensive, anything goes. But when serious work is being done and you don't want any distractions, you need to turn off the AIM (or go invisible), crank up the mood music, and make it work.
When lyrics are ok and you just want to relax and work?
Rush, Yes, Zeppelin, Marillion, Blue Oyster Cult, Floyd (any), Fleetwood Mac, etc the list goes on forever.
Those who like Floyd and Rush/Yes (any of the classic prog rock) need to give Marillion a shot (older stuff not the new).
You'll wonder how you survived so long without ever hearing them before.