I like to keep things simple but my list of things to install are:
HTC Home
http://www.pocketemu.com/download8.html
Google Maps
Windows Live Search
Microsoft Voice Command
Quick Menu (Instead of X-Button)
http://www.freewarepocketpc.net/ppc-...menu-v2-7.html
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Advanced tweaks that I enjoy
No2Chem's WM6.1 (Currently using build 5047 but will soon upgrade)
DCInoBar (removes the contacts/calendar buttons on the today screen however the soft keys still work but you get more screen space)
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Thats about it, if they don't have a link a simple google should work.