I'll definitely be attending in 2012.
That's not entirely fair though, insofar as I'm a sucker for a Sussman talk.
Beyond that, I'd have to say Sam Aaron's Overtone presentation @ Clojure Conj 2011.
At the moment, it strikes me that the obvious common element of both talks and speakers are their absolutely infectious enthusiasm for their respective specialties.
We were fortunate enough though to have the excellent YOW conference with many excellent talks, particular stand-outs coming from Simon Peyton-Jones and Mike Lee, but the absolute best talk (not necessarily the best tech, it is Perl after all) was Damian Conway's flabbergasting "Temporally Quaquaversal Virtual Nanomachine Programming In Multiple Topologically Connected Quantum-Relativistic Parallel Timespaces...Made Easy!"[1]
[1] http://www.yowconference.com.au/YOW2011/general/workshopDeta...
http://www.infoq.com/presentations/Functional-Data-Structure...
Running a Startup On Haskell: http://www.infoq.com/presentations/Running-a-Startup-on-Hask...
Also "Hammock Driven Development" by the same gentleman.
I have never had my head crushed by so much actionable info in 1-2 days. The entire conference was worth it by the time the first speaker had done his session and it kept getting better.
I'm looking forward to Microconf 2012.
Also, my best advice at any conference is to take notes. I took comprehensive Startup School notes, and reviewed them later. I never would have gotten so much out of it if I hadn't.
Learnt quite a bit from these two talks.
Morten Lunds talk at the Power of 1 conference in Battersea powerstation