I decided to make this because I was listening to one of my favorite [guitar] riffs of all time, and I would love to know what everyone's favorite riffs may be.
At this moment, my favorite is the last quarter or so of this live recording of Muse's "Knights of Cydonia". Great guitar in general, loads of triplets, but this recording in particular really stood out to me.
(Starts around 5:04, if you just want to get to the goods. It's even in HD!)