MouseExtender pops a customizable grid of program directly under your mouse pointer whenever you press the middle button. When you select a program, the window disappears until you need it again. It's that simple.
There's a lot to like about MouseExtender. There's no installation needed; the program is composed of a single EXE file and a configuration file that tracks what programs you've added to the grid. It's free. You can specify the width from 1 to 10 icons across, and you can load it up with apps, folders, and files. And unlike some app launchers, adding programs to MouseExtender is quite simple; just pick the app from a list of running programs.
Even given the cool taskbar improvements in Windows 7, I have started using MouseExtender on both Vista and Windows 7. There's only one feature it needs badly: The ability to rearrange icons once they're added to the launcher window.