Where is the unavailable disk space? I recently uninstalled a 120 GB windows 7 (installed and uninstalled via boot camp) on my Mac mini machine. I suspect that part of the disk space used in that installation has been made unavailable. Look at the following terminal commands:

$ diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk0
   1:                        EFI                         209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            389.0 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3

$ df -h
Filesystem                       Size   Used  Avail Capacity  iused      ifree %iused  Mounted on
/dev/disk0s2                    362Gi  319Gi   43Gi    89% 83772049   11198653   88%   /
devfs                           200Ki  200Ki    0Bi   100%      693          0  100%   /dev
map -hosts                        0Bi    0Bi    0Bi   100%        0          0  100%   /net
map auto_home                     0Bi    0Bi    0Bi   100%        0          0  100%   /home


The results above show that I am missing 110 GB of disk space. I know that the operating system itself uses space, but I very much doubt that it is that much.
It looks like uninstalling Windows via bootcamp did not merge the space reclaimed by removing the old windows partition into your Macintosh HD one. In order to do that you can use the Disk Utility.

You can simply drag your Macintosh HD partition bigger and apply it. Here is a tutorial on how to resize partitions with Disk Utility