We recently mentioned Freeverse's Think, a little utility for helping you concentrate on one task by hiding away all the other windows besides the foreground application. Apparently somebody else liked the basic idea, but didn't quite like Freeverse's somewhat involved execution and so has whipped up a similar but more stream-lined utility called Isolator. Isolator sits in your menubar and, like Think, will isolate the windows of the foreground application by hiding all the others and bringing up a solid color shade over the desktop (though you can adjust the transparency of the shade and even set it so you can sill access the desktop icons). You can also set a hotkey to turn Isolator on and off (F8 by default). I like the idea of a menubar utility of this sort, but if there's anything I don't like about Isolator, it's that when you turn it off the applications it hid are still hidden.
Isolator is a free download, but the developer is requesting donations.