I recall team 67's 2008 robot as having one of my favorite linkage mechanisms (at least conceptually... implementation looked painful
). Spring loaded extending member in a single DOF mechanism to achieve a very unique path and stay within size constraints, very cool!
Also a big fan of 1625's over-center launching mechansim, though I've yet to use it on a robot. I'm sure a time will come.
The Thunderchickens arm from 2007 is very unique, and another favorite of mine. I used it as one of my "pick any mechanism and do a report on it" style of exams for free-body analysis in college. I wish I remember more details of my analysis, but I wasn't very good at documenting things back then.
67:
http://www.chiefdelphi.com/media/photos/30680
1625:
http://www.chiefdelphi.com/media/photos/31538
Short analysis on 217's arm attached as well.