My MacBook just said "Startup disk almost full." Other than just deleting files, what can I do?

You don't really have many options if the problem is your drive is too full -apart from compressing files using Stuffit or Zip - you've got to get rid of stuff. But you could have files lying around that you may not know you have.

Make sure you've not got "encode" information still stored from iDVD or other DVD making software - sometimes you forget it's there and they take up loads of room. In the program, there should be a "Delete encoded assets" option or something of that nature.

Also make sure you have deleted files from your Sent and your Trash folders of your Mail program.

Also make sure you have deleted your cache from your internet browser.

Also back up any docs you don't need to hand onto blank CDs or DVDs.

I find Stuffit does work well too though - you can shrink a 2Gb file down to about 100Mb - however the program you need to compress costs money - but not much.

You may find something freeware on Download.com though.

Well, you could burn files to DVDs or CDs if you don't want to delete them. If you don't want to replace the hard drive inside your Macbook with a larger one (the Macbooks do have user-replacable hard drives), you could get an external hard drive with a large capacity for storage.

Aside from those, there's not a lot else to do..