I have discovered the awesome Windows 8 “storage check” on my Lumia 920. The new tool is available in the latest software update. It is really, really good. Storage Check gives an overview of disk usage on the phone and allows for viewing a break down of the Apps installed, and for some Temp files clean up.
It is a good looking graphical overview of how much space is in use, and of how much is free or available. For example, my phone has 29 Gigabytes of storage (likely it’s 30 GB total, with 1 GB going to the OS). 16 GB is in use. You can see the breakdown below. The Details section shows specifics, like how much space is taken by Photos, Email+contacts, Office Documents, Ringtones etc.