"neat" and "useful" mean different things to different people.
How about you tell us what you feel you are missing in your UI, and then we can help give specific suggestions.
Other places to look are...
AddOn Survival Guide (the most popular addons):
http://www.wowinterface.com/survivalguide.php
Vranx.com:
http://www.vranx.com/index.htm
Pick of the Week:
http://www.wowinterface.com/pickofweek.php
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"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff,
The Tao of Pooh