Dropping this in incase anyone finds it useful. I have not tired it yet, but it looks like it might be useful.

http://www.uderzo.it/main_products/space_sniffer/

Well, I don't know how well that would work on an SSD, though I expect there's no difference, given that the functions of SSD/HDD are identical, but I can say that I use a very similar program (that was ~NOT~ freeware, BTW) called Treesize Pro, and it works the same on SSD's that it does on HDD's (though it runs a ~LOT~ faster on the SSD's).