Quit Anything is simple application that can be used to quit processes. It lets you quit multiple processes all at once without having to switch to each one, and also lets you quit background processes (a.k.a., 'Faceless Background Apps' or 'Daemons').
Please note that there are many system processes which run under OS X which cannot be seen by AppleScript and so this program can't actually quit anything as the name suggests. (Hey, the name was accurate when it was first created. :-) )