Visor, the new application from Blacktree, creates a half-screen terminal window that pops up with the press of a hot key. This terminal is persistent, so when it’s in the background, it just keeps on going and going and going.
Very clever little hack, and extremely useful if you’re prone to bouncing between the terminal and your desktop.
The only problem I’ve had with it is that it’s only one window. So I invoke screen as soon as it starts up, and that pretty much takes care of it.