MacOS X defrags files over a certain size (>1MB?) in the background anyway, so this is just about space.
Delocalizer gets rid of extraneous language files (from memory, getting on for a Gig), and you can manually delete the trial software.
I agree with the post further up about print drivers - if you have a lappie and you're all over the place like I am, you never know when you might need one.
Garageband (which I've never used - personally no call to) is worth at least 2GB in space when that goes.
Even on a 120GB drive, 3GB is not to be sniffed at - that's room for 350-400 songs or 1000 photos. 😉