It's always seemed to me that the image that comes from the built-in camera on my MacBook Pro should be more adjustable. We've previously mentioned iGlasses, a webcam utility (from the makers of the handy Call Recorder for Skype) which provides all of those missing controls. The utility recently updated to version 2.1, and adds a zoom button, stability improvements and compatibility with more applications.
iGlasses 2.1 lets you control color, exposure, zooming and cropping of your iSight (or one of several other webcams). It also provides several color adjustment "effects", if you're into that, and it's AppleScript-able so you can automate settings. Personally, I'm mostly interested in zooming and controlling lighting/color settings, which it handles quite well. Once the free, 7-day demo is installed, the adjustment palette shows up in most applications that use the iSight: iChat, Skype, Skitch, Pixelmator, Photo Booth and about 60 others.
iGlasses will set you back $9.95 and a free demo is available. The demo can be easily uninstalled by running the installer and clicking the "Uninstall" button.