Everyone here has already mentioned all the good moments. The nexus still is the most memorable moment for me since it was so unexpected. Although Danielson and Wade, the best of that bunch, are still around, I am still a bit peeved about how badly WWE managed that angle.
One moment that no one has mentioned so far is Batista mini heel run before he left the company:
There are of course multiple moments with punk. Another moment that no one has mentioned so far is Punk cutting promos in the middle of Royal rumble 2010.
Let's not forget Bret hart 2011 return:
And Shawn's retirement speech:
Very genuine and heartfelt.
The best moment so far in 2012 for me has been the whole post WM Raw where the whole crowd was chanting Danielson's signature phrase throughout the show. That whole raw was crazy.
[ame="http://www.youtube.com/watch?v=NNxqopColTc"]WWE Raw 4/2/12 Full Show (HQ) - YouTube[/ame]
Oh yeah, and there was that Benoit incident. Memorable for all the wrong reasons.