There are a lot, actually... the obvious but nonetheless applicable NPCs would be Jiub and Caius Cosades. Aryon's up there too, along with Therana and Fast Eddie. Vivec and Dagoth Ur get tossed in too if they count as NPCs. From there favouritism tapers off slowly.
As far as unconventional NPCs go, Dagoth Ur would fit into that category, if he qualifies as an NPC, but there are no NPCs I can think of without quest significance who I really pay attention to. Plenty are alright, but hardly favourites.
~Master Nomas, Chief Gnome Emperor of the Bug Council, Dexter District, pit of Tel N'gahtel, South Dexter, District of Dexter, Province of Iggerty