Here is a way to generate simple, wonderful pink noise (with a slight tremolo) from the commandline, if you have sox installed. It somewhat mimics the sounds of waves on a beach - I find it very relaxing.

A nice side affect (and the reason I played around with it originally) is that it helps mask tinnitus when it gets too annoying (I find that if tinnitus flares up too loud, it can make it more difficult to fall asleep).

The cmdline:

  play -t sl -r48000 -c2 - synth -1 pinknoise tremolo .1 40 <  /dev/zero