I guess it would be lazy to just say, "The entire cast of Dragon Age: Origins", so I'll think that instead and put some actual effort into coming up with different examples. How about...

A mad scientist, like Kang the Mad from Jade Empire. Someone who's SUPER EXCITED about the mind flayers and the tadpoles and stuff because it's all so weird and interesting. They can join Astarion on Team "We should totally use this thing what do you mean it's a bad idea."

A dutiful do-right veteran with the voice of reason and bubbly and perky optimistic comic relief, because I love those tropes and Tzelanit will be so annoyed. grin

Someone alien. I was hoping Lae'zel might fit this role, but she's far too "normal". I want someone whose way of thinking is completely baffling at first and over the course of the game we work to wrap our minds around their minds - sort of like Sten from Dragon Ag I mean, uh, Yuun from SWTOR or Grieving Mother from Pillars of Eternity I.

A kid brother/sister type. Someone who's equal parts annoying and endearing, someone who's not a world-weary adventurer with pages of backstory to throw at you, someone who's actually a little lost and freaked out in this situation and looking to the PC for guidance. Imoen is the obvious example, but I got the same vibe from SWTOR's Guss Tuno and Nadia Grell, or the famous Deekin Scalesinger (doomity doom dooom).

A cat? My camp needs a cat, Larian.