Bach, preferably short pieces I know well; failing that, Mozart, likewise. Either can serve as a pleasant diversion for those parts of my mind which get bored and need something to occupy them while I'm hacking, without requiring anything in particular from the parts of my mind which are focused on my code. (I'm not doing either composer any favors from an artistic perspective, I realize, but it's not as though I don't enjoy their work for its own sake as well.)
Depends on what productive means.
For pure coding, when I want to create a bubble around me I usually listen to trance.
I had a playlist of more than 200 hundred remixes of satisfaction back in the days. Good way to code for 5 hours without putting your eyes off the screen.
When I need to think / design, it is usually some chill out (like enigma).
When I'm coding I either use; www.getworkdonemusic.com or www.mynoise.net. GWD is just a soundcloud interface with some fast vocal-free techno beats, so it pumps me up while not interrupting my focus. I get frustrated with it because it breaks a LOT. I'd say ever 5 or 6 songs it will finish playing a song and fail to load the next which is absolutely attention killing when you're in the middle of a creative rush.
Mynoise.net on the other hand is absolutely incredible but it's ambient sounds. The guy who runs it is a sound engineer and he updates the site frequently with new sounds. It's seriously great. Ive donated multiple times. He now has an iPhone app as well.
I absolutely love his binaural beats, airplane cabin, sail boat noise machines.
I have a playlist called Tasteless Rap on Spotify that helps me focus. Solid beats, lyrics that are pretty easy to memorize (and thus not get too caught up in), and fun. I've got it arranged into a pretty good ebb and flow of energy, so I don't get worn out halfway through. I also second @gadders' birdsong comment: it's quite lovely, especially with coffee/tea. Which reminds me, Coffitivity has been excellent for tuning out the distractions of our open plan office (it's not fully open, but the room I'm in has 4 other people with no blockage of sound or sight lines and is quite busy).
BBC World Service/CBC Radio One Ottawa. The Commonwealth news media usually are more int'l than US media and focuses more on disasters such as raping, pillaging and military conflicts that's happening.
Gives me both a sense of schadenfreude about how I won the birth lottery to be born in the US; and also a sense of urgency to make use of my time more wisely vs. posting links on someone's wall when kids from schools are kidnapped for marriage.
If I am in the office at work and I need to get things done I have some over ear headphones which are really good at noise cancelling.
I will just sit there with them on listing to nothing. Its nice as it means people will not come over and bother me; also I do not hear others working.
Oddly enough, I find movie soundtracks to be the single most distracting music selections during work. I constantly find myself zoning out and thinking about movie scenes. For me, a soundtrack carries a heavy emotional weight similar to watching the movie itself. In the case of LoTR, I get this crazy nostalgic feeling and have a strong desire to watch LoTR again. Great movies.
I find that albums I have listened to more than 15 or 20 times help me focus the most during work or study. New albums and hip-hop both tend to distract me.
nothing: anytime anything is on in the background I find it to be completely distracting. This includes classical / jazz and any of the obvious non-offensive niches.
I work in an office of 8 people. 5 listen to music, 3 of us prefer silence.
