My C:\Users\[username]\AppData\Roaming\Bitcoin directory has ballooned up to approx. 17 GB and I feel like this is larger than it needs to be...
You might have the old block database, which you won't need anymore.
I don't remember though which folder it was, but it should be a second that has a few gigs of files.
Also I believe if you have NTFS (and most windows users do), you can order your system to compress the folder - that would also save you some space.