iSerenity

Here's a soothing, easy-to-use tech tool: iSenerity. Want to mask office noise, loud conversations from the office next door, get a baby to go to sleep, or just relieve a little stress? This is an on-line white noise machine, with all sorts of options. You can play ambient noise mimicking waterfalls, thunderstorms, crickets, typewriters, library sounds, birds, even (and this is my favorite) the old-fashioned sound of a number two pencil writing on a piece of paper. How ironically low tech.

http://www.iserenity.com/

All the sounds come with a visual component as well, in the form of a slideshow of still pictures relating to the sound, but it seems to me the best use of this is to have it on in the background on a minimized browser window as you work on other things.