A GREAT list from Mac Tricks and Tips:
The menu bar, if you didn’t know, is that long strip across the top of your window. It contains space for adding your own little applications to do various tasks for you. This include a variety of things, from the mundane such as telling you how many unread emails you have, to the complex such as cleaning out your computer. Each application posted here is designed to run from the menu bar and not as an application. Programs which run in the dock, but have a menu bar icon do not count. They have to run 100% from the menu bar.
(See them ALL HERE)