I find that music with "words" is distracting. When I really need to concentrate and get some serious jewelry made, I'll go with Enya, Yanni, Narada, or some other New Age group. Can music be relaxing and stimulating at the same time? You bet!
Music is soooo important when I'm busy making! This last week it's been a lot of: George Harrison, Billie Holiday, The Shins and Elliott Smith. (Amy Winehouse made it in there too!) Fun Fun Fun!