I'm using Fedora, and love the graphs, so my favourite GUI tool is: Disk Usage Analyzer. Just fire it up, select the location, mount point,... you want to perform inspect. Here is its result:

Just look at some location on the top and confirm that those have normal usage, otherwise you can nuke all useless contained items to recover some precious air.

Forget the X interface, an alternative command for the console is: du

It's really simple to use, just typing something like this:

$ du --max-depth=1 -m /home/you/

Happy cleaning day!