1523's catapult in 2006 instantly came to mind for me.
http://www.chiefdelphi.com/media/photos/22906
https://www.youtube.com/watch?v=NlwqXk1vG9s
http://www.thebluealliance.com/match/2006gal_qm41
272's electromagnetic clasping mechanism for their launcher in 2008.
http://www.thebluealliance.com/match/2008pa_f1m2 (yellow robot)
Also note, that 341 dropping the ball and having it roll across the line at the end of the match was the margin for victory. Absolutely nuts match, one of the best of 2008.
1731 had a slew of interesting features in 2008. They were one of only a few teams who acquired the ball without any active mechanism (25 being the other that comes to mind). Their launcher provided mostly vertical momentum, and they relied upon their drivebase's forward momentum to hurdle the ball over the overpass. Their hybrid mode signalling device wasn't an IR transmitter, but rather a series of different colored lights that their robot would detect. One of my favorite bots of all time, and one of the best to not win a regional (2x finalist).
http://www.thebluealliance.com/match/2008oh_f1m1 (red alliance with yellow bumpers)
The Enginerds have had a few really creative bots, but their 2010 one was really neat. They had their rear mimic the actual hanging bar in order to suspend their teammates, as well as their mid-season adjustment to their ball deflector that allowed it to function while hanging.
http://www.chiefdelphi.com/media/photos/35831
http://www.thebluealliance.com/match/2010gl_qm88
First brain dump of unique robots complete. Will try and remember more of my favorites later.