My C: partition on Windows is too small so sometimes I have problems with space. I have made a recent discovery that not only Windows itself but also Visual Studio 2010 is an out-of-space-situation helper.
C:\ProgramData\Microsoft Visual Studio\10.0\TraceDebugging
This is where you may find lots of files which will not be probably needed anymore. I've just deleted 2.5GB from there. I've got shocked it would be that much.
I recommend WinDirStat. It's a cool and simple application that helped me to find the path given above.