"Isolator is a small menu bar application that helps you concentrate. When you're working on a document, and don't want to be distracted, turn on Isolator. It will cover up your desktop and all the icons on it, as well as the windows of all your other applications, so you can concentrate on the task in hand."

Interesting idea, but it doesn't appear to work.

"Menufela is a haxie that hides your menubar, giving you back those pixels you've never been able to put to use before." - appears when you hover over, frees up a surprising amount of space.

High Priority is an inexpensive Mac OS X 10.4 or higher menu extra whose sole purpose is to help you manage your To Dos in a simple, intuitive, and pleasant manner.