Visor

I just found out about Visor from the makers of Quicksilver, which is a persistent terminal you can invoke via a hot-key combo.  Upon hitting the hot-key, a terminal slides down and fills half your screen.  Pressing the key again slides it back out of view.

I love this because I have way too many terminals open across all my spaces.  I run it, invoke screen within it, and bam, I'm set.