TUAW's Daily Mac App: QuitAppsMBI
Quitting apps quickly can be a pain. If you've got loads open, but you want to quit them all fast, the best way has been Cmd+Tab then Cmd+Q. Now, the free QuitsAppsMBI app makes quitting some or all of your apps a breeze.
A menu bar utility, QuitsAppsMBI sits patiently waiting for your command. Click on the icon and a drop-down menu featuring all the currently running apps allows you to quickly quit individual apps or quit them all at once with one click.
QuitsAppsMBI even allows you to quit apps you couldn't normally. Things like the Adobe Update notifier (a personal bug-bear of mine) and other unquittable menu bar and background apps can all be quit from the drop-down menu. This is both a feature and an issue for QuitsAppsMBI, because there aren't any settings for excluding apps from the "Quit All Apps" command, which means if you have things like tablet support programs, Xmarks or other background apps, they will all be terminated as well.
If you need more functionality such as excluding some apps from the "Quit All Apps" command, Limit Point Software offers a paid-for version of QuitsAppsMBI simply called QuitsApps, which is available for US$9.99 from the Mac App Store (trial available on the Limit Point Software website). But for just quickly quitting a few or all of your apps the free QuitsAppsMBI gets the job done.