I enjoy my Ratatat station on Pandora. It has very few vocals to distract me. They are just a torrent of noise without much I only play it when I'm working so my brain knows what time it is.
If you listen to metal, I would recommend Machine Head and Lamb of God as two excellent band for "work mode".
I recently discovered dubstep and think it's great work music as well. I would recommend checking out iTunes and Pandora to start finding artists you like, some of my favorite stations are Defiant radio on iTunes and Destroyer.net.
Hmm, I am not an expert on dubstep, I just have a mix that a friend sent me that is mostly Dieselboy. It might be considered drum n' bass, not dubstep, but that's just what I call it because it's got that wahwahwah sound and I have no idea.
Edit: Oh yeah, I can give a shoutout to Aaron Static though, I met him through EVE Online and he comes out with great new "Power Hour" mixes every month: http://aaronstatic.com/
Although not dubstep I really like Soma.fm, especially Mission Control. I'd recommend Hype Machine for finding new artists. I've really been digging Boadecia by Mason which I found on Hype Machine.
If you listen to metal, I would recommend Machine Head and Lamb of God as two excellent band for "work mode".