When I used Palm OS Treos one of the first apps I always installed on new devices was Hi-Launcher. Now that it's finally available for WM, I downloaded it and am very pleased with the results so far.

www.hilauncher.com

Hilauncer was an app that added a cascading menu to the Palm OS.
Windows Mobile has dozens of apps that do the same thing, but none of them matched Hi-Launcher's functionality and I ended up uninstalling every one I tried.

HiLauncher is different because:

1) It was very easy to customize with a built-in menu editor that allowed you to change the size, color, contents, etc.
2) You can add a shortcut to just about anything - files, settings, contacts, make shortcuts to call someone or email someone
3) It allows for multiple levels in the menu system. Most other WM apps only allow for one or two sublevels.
4) Most importantly - it does all this without hogging up system resources every time it's launched. The menu comes up instantly and you can get to just about any task in one or two clicks.
5) It also seems to be customizable enough to have an icon-based task manager and recently used apps all integrated into the main level of the menu - meaning both are just one menu button tap away.