Low C: Drive Storage Space?

I'm obviously brand new to the forums so I hope this is the right place for this. I should start with my type of drive; I have a 120gb Cherryville SSD from Intel serving as my C: Drive. Just the other night I had approximately 43GB left in my C: Drive (note this is incredibly low as well, but I was content). Last night I checked again and saw that I was down to 25! I performed a disk defrag and that actually decreased my storage to 23! I am absolutely puzzled as to the cause of this.

The only thing I have done between the time that I had over 40 and last night was update my visual BIOS (having nothing to do with my C: Drive at all) and download a simple XML update for Microsoft Expressions (which was measured in kilobytes). Granted I have done my fair share of updating .net framework and various other updates, but all of my major programs are on my hard drive, not my SSD. To put this into visual perspective, I'd like to share a photo showing around 25GB of space taken that is absolutely nowhere to be found, I find it hard to believe that Windows and a few programs can take up nearly 90GB of storage.