I prefer silence, but since the open-plan fad holds sway here, I've found rain to be the most effective substitute. The best rain track I've found so far is 57 at http://archive.org/details/Sounds_of_Nature_Collection
Its called conditioning the mind.
Its a bit like the right pane in eclipse, In years I never remember using it even once, yet its absence will irritate me.
Ever get that feeling sometimes when you are surrounded by people in a noisy place and yet after sometime sort of don't even feel that is disturbance.