Researchers at University of Urbana-Champaign found that productivity of workers increased in a coffee shop environment that was not too loud or not too quiet. There is an interesting NY Times blog describing the effect.
Interestingly a group of people have taken that to create an app that plays the recorded background noise back, with the hope that it will increase the listener’s productivity and creativity. The sounds are available for free on the Coffivity website too – the link is below. Try it out.