OS X takes up a good amount of space. use
Monolingual to clear out unwanted languages (make sure everything in the architectures tab is unchecked, though) and maybe thin out your printers folder in HD > Library > Printers.
most people who've had problems with Monolingual don't read the accompanying documentation/FAQ and end up deleting some important system files. this bit from their
FAQ is pretty straightforward:
Q. Should I remove the non-Intel architectures on my Intel based Mac
A. You can use Monolingual to remove non-Intel architectures for your installed applications (even if some of the applications are PowerPC-only; Monolingual is smart enough not to remove PPC forks if those are the only ones in the universal binary). However, you should not strip the System frameworks if you want to use Rosetta. Rosetta needs the PowerPC code for all frameworks used by the emulated application...