Launchy is invoked/dismissed by a hotkey (alt+space by default). It is pre-set to index your start menu links, but can be customized to index any location on your hard drive for any type of file.
This is a very interesting launcher that takes very little system resources to run. It is a must if you, like me, have a ton of installed applications and a lot of files that you work with.
Go to download page for latest version. The program home page.