I would start with your documents area. Any big downloads you don't need anymore? Anything you can move to a memory card?

Then if your browser has such a setting you could try clearing browsing history, etc.

Do you have any apps storing data in the device's main memory rather than on a memory card? If so, can you move the data? I'm thinking e-mails & media files mainly.

Hopefully that should get you enough space to work the Application Manager again. There, you can sort your apps by size and delete those you don't need.