ClearTemp is an excellent freeware application for Windows Mobile 5.0 based mobile devices that can scan your mobile system and delete unwanted temporary/unused files as well as registry keys/values associated with uninstalled applications/themes.

It allows you to clear the following items:

Recent Program List
Internet Explorer Mobile visited URL Address History
Boot count
Temp folder
Internet Explorer Mobile cache and cookies
Opera mobile browser cache
Minimo mobile browser cache
Netfront mobile browser cache
Mail attachments/Large mails in Storage card
Unwanted registry entries associated with WM5 Themes.
Unused registry associated with uninstalled programs.

You can also add custom folders to scan and also change the location of the mobile device’s temporary folder

Download here