Merciless Cremator, Captain of Squad 2. The guy who silently appears, randomly drop off a topic and quickly disappear again.
For canon arc, I must say I also love the Fake Karakura Town arc (idk how far it extends). We got to see Soi Fon's bankai, Shunsui and Ukitake's shikai fully explained, and some awesome Kido by Hachi and Urahara. The HM arc was also quite nice, because of the Byakuya and Mayuri fights. (I'm not a very big fan of Ichigo and Kenpachi fights, yeah).
The only down thing about the FKT/HM arc is that it has little Unohana in it. =( Ah well, at least we saw her traveling with Ichigo and healing Hiyori. =\