Download the trial version of memmaid:
http://www.dinarsoft.com/memmaid/
Install it, then when you run the program, select the 2nd to last tab. From the drop down at the top left, select 'Storage Usage' if it isn't already selected.
This may take a while..
It will then show you what folders are using up the most space. I recommend removing your SD card before doing this so it doesn't search it.