Old thread, I know, but I remember it from months ago and was curious to see how it turned out.
Disk Inventory X is a good freeware program to find out where your storage space is going. I use it very often.
This is what I used. I took my MBA to the Genius Bar for service, and while I was there, asked about all the "Other". The genius bar guy downloaded Disk Inventory X onto my MBA, and we were able to see what was up. It's a cool application, because it shows you in picture form what is taking up space. When you click on each rectangle, it highlights on the associated list what that rectangle represents.
Right away, he showed me that I had over 18GB of iPhone backups that were unnecessary to keep. I also have over 9GB of saved Mail.app emails on my MBA. Since all of my email accounts are Gmail, it actually didn't occur to me that they were being saved on my Mac for offline use.
I now have over 70GB of space free on my 128GB SSD, so I'm planning on moving either my iPhoto or iTunes library from the external HDD I use onto my main drive.
Hopefully this helps someone.....
