VoluMouse is a tiny little utility that let's you adjust variable commands that are all dependant on one thing: the scroll wheel. As you can tell by its name, it is mainly about adjusting the volume, which is extremely handy. Like for example, on my main computer, I actually have two sets of speakers: one in the flatscreen monitor, and one regular pair of desktop speakers. My flatscreen speakers just suck, but that's another story. Anyway, I have it set perfectly where the balance is between monitor and desk speakers, and I hate messing that up, plus if I want to turn them both down, I have to click the icon in the taskbar, and all that. OR I can hold down Shift and Control and scroll up and down.
So that's my use for it. Basically you can set alot (up to five, I think) rules that can apply to all different sorts of volumes: Master volume, Front, Back, Wave, Line in, Recording level, etc. It can be set to different conditions such as when Alt is held down, when Shift is held down, when iTunes is in focus, when the cursor is over the taskbar, etc. You can also adjust how many steps it moves with each scroll. I don't exactly understand the intervals, but just mess with it until you find one you're comfortable with. You can even set it negative, meaning that scrolling up turns the volume down, and vice versa.
It can also be used to adjust screen brightness and window transparency. Like I said, it does more than just volume. You can even download a plugin (which I just figured out about) that can eject your CD drive! It hasn't worked the best for me, but I just figured out about it. I think messing with the "Steps" setting will make it work more reliably.
It also gives the option of using hotkeys instead of the scrollwheel, for those who want that instead. Really, this app saved me because I used to have a keyboard that had an eject CD button on it, and volume controls, but it stopped working. Now I can do it from my mouse, and it runs from my taskbar, is highly configurable, and runs under five megs.
I can't live without it ever since I discovered it.