OK, here's something I've always thought was cool and am seeking a project to use it on:

http://leftlogic.com/lounge/articles/jquery_spy2/

Basically, it shows a set of self-updating data with "older" items fading out of view as time goes by. Not sure what I mean? Check out one of the examples:

http://leftlogic.com/jquery/spy.html

Recently FriendFeed deployed something like this. Here's Robert Scobles, usually pretty active:

http://friendfeed.com/scobleizer/friends/realtime

No fade-out there, but you get the idea. And hey, they use jQuery, too!