MacBook :: Hard Drive Space Doesn't Add Up?

Im having a problem with my HD on my MacBook Air 2011 with 128Gb SSD and Lion. 

Since about a month after I purchased my computer, I started to notice low HD space. I started managing it but couldnt keep it with more than 15 Gb of space. I transfered my biggest file, a Parallels Desktop virtual machine to an external HD. I have disabled Time Machine and have removed most of my files from the computer. My User folder barely uses 27 Gb of HD Space. The Get Info shows that I have used 90.84 Gb and have 29.63 Gb Free. But when I try to add all of the folders from the HD (Applications, Library, Syste, Users) it comes with a 42.42 Gb used number. 

I tried lots of programs like Disk Inventory X, WhatSize, OmniDisk Sweeper, etc, and all come up with an aprox. 43.38 used Gb number, so there is no discrepancy between these programs and what Finder is telling me. Here is a screenshot I took with WhatSize.

Where is the rest of the space going? Im lost on what to do to empty space.