If you really just got your MacBook, like I did mine, you could just do a clean install of OS X, select custom install, only pick the languages and software you want/need, and save a ton of space. I kept all the software, but left off all languages other than Japanese, and I saved something like 4 gigs of space.
If you delete the sample tracks in garageband you get a chunk back, but don't delete the loops if you are into any type of music/sound creation.
Oh, yeah... congrats on your new Mac!