Sony Ericsson Themes Creator

This tool is ideal to create thm files.

Made by SE itself.

Download here.

Sony Ericsson Layout Generator

Not all gfx packs but some also contain layout.xml to tweak where the elements of the screen go. Like move battery for instance.

Download here.

Menu Editor

Quite obvious what it is. Get it here.

SE Theme Tools

The only purpose of this application is to link themes to flash menus. (What the SE-lifestyle Flash Menu Picker does on the phone alone.)

Download here.