There's still a few favorites I'm hoping for, but I think the Tricous would be a perfect fit. Olive Spector would work, too.(although they kind of touched on her in LL with a relative) Of course, the vendors from Sims 1 would make sense, Vicki Vampiress, Apothacary Todd and Fairie Queen Mara.
For me, it's the Tricou's hands down.
Who would you like to see make a comeback in Sims 3?