Running out of "App Storage"?

My device (HTC Evo 4G LTE) is battling running out of "app storage". From what I understand, the storage in my device is split in three ways.

(1) App storage, a 6GB area of onboard storage where apps are installed by default.

(2) Phone Storage, a 10GB section of on board storage used for data files and apps can be moved here.

(3) ExtSD Card - My physical SD card I have in the device.

My issue is that the app storage of only 6GB is almost constantly full. I regularly move apps from App Storage to Phone Storage and even though I do this, I am always a handful of megs away from it being full. According to my devices storage page (Settings ->Storage), only 1GB of that is actually apps. The other 4+GB is "Other".

My device is not rooted (and I do not want to root it at this time). How can I find out what this "other" is to clear some of it out?