Not surprisingly, there've been some previous threads on this. See music choices.. and, more recently, Music to Code to. Since tastes (and the mix of monks here) change, it's fitting to revisit this now and then.

I favor contemplative music while designing and coding. Gregorian chants fit the bill nicely, or some of the less irritating Philip Glass or Steven Reich. Something at a nice, steady pace that doesn't interrupt, or disturb, or otherwise leap out to scream "Pay Attention to ME!".

For debugging, I like to pick the pace up a bit. Rossini's William Tell Overture is good for that "thrill of the hunt" one gets when hot on the trail of a gnarly bug. Drumming music works, too.

Lately, though, I'm relying on a really loud ventilation duct to shut out background noise. It's a steady "whoosh" that's somewere between a waterfall and a very windy day. Once the facilities folks get around to fixing it, it'll be back to Gregorian chants.