Any way to search based on file size?

These are good ones:

http://www.derlien.com/
http://www.id-design.com/software/whatsize/

However, a lot of that room is probably taken up by the default install. You can forum search here for great threads about thinning out the default install if you need to do that, but many people are very tempted to go out and use Monolingual on their new Macs, and I just want to warn you to be careful. They inevitably come back complaining that nothing on their Mac works anymore. It's gotten to be that if someone has an Intel Mac and none of their applications will run, the first question is, "Did you use Monolingual?"

 

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:

 

This is very true. There's nothing inherently wrong about Monolingual. It's just that newbies do this over and over again. There are multiple threads in MR weekly with some new user who has b0rk'd their MBP.... But it absolutely is not the Monolingual author's fault.