OneNote Instant Navigator
We use OneNote a LOT at work. Once you get used to it, it is basically an offline Wiki. You can link all over the place easily, store it on a server to share, and work offline. I love it.
But once you get to using it this way, you end up with a whole bunch of notes. It can be hard to find something when you need it.
Enter OneNote Instant Navigator...
Assign a hotkey (I use Win+I) and now you can very quickly get to any note you want. I love it.
UPDATE: Forgot the link: http://i-navigator.hut2.ru/