Android - What can I do to manage my phone's internal storage?

I'm using an app called DiskUsage which helps visualize what's using both my internal storage as well as the SD card.

Most of the apps you have listed are big because they are storing data. The apps themselves are not that big. I would encourage people to check large apps (you can sort by size in the manage applications area of the settings). Chances are you can clear out the data and reduce the amount of size very easily. Most of the data for those apps especially is email and data that are old and don't really need to be on your phone.

To better control your Gmail storage in Android you can adjust the number of days that are synced. The control is in a place many people don't think to look; it is in the "Labels" section. In there you can adjust syncing to a certain amount of days; I use 2 days. Depending on your daily volume you may need to go to 1 day or could go up to 10.

There is also granular control, you could keep your starred emails around for 4 days while everything else is at 2 days.

It is all about Gmail's label setup. It is better to think that you don't really have an inbox, you have emails that are labeled "inbox".

Hope this helps out! Once you make the change it will sync up and reduce your storage right away. I recommend turning off and on the phone after making the change (just like a computer, the Android phones like a reboot from time to time).