You've got Desktops!

Unix GUIs have long had “virtual desktops”, where you can switch between multiple screens on one monitor. I’ve used this, but never found it that useful, mainly because you’ve just got a bunch of different Terminal windows open, not full-blown graphical apps.

Codetek makes a product for the Mac that is simple and actually usable/useful: Codetek Virtual Desktop.

Basically, you can easily drag the windows of an application off one side of the screen or the other, and they pop into the other desktop. I keep a bunch of browser windows and my IM app open in one desktop, and whatever I’m working on in the other.