This week's TechRepublic tip is Configure GNU Screen to handle multiple terminals. Screen is an awesome program that works great on Linux on OS X. The tip is pretty much platform-agnostic; it works well for both Linux and OS X (I use it on both). The really great thing is to be logged into screen handling your mail/IRC/compiling/etc. and being able to ssh in remotely and check everything at once via one simple screen call.
Along with openssh, screen is probably one of the most useful CLI tools you can get.