Some people have mentioned Shika and Hinata; I think Naruto would have been better off (in the sense of having less emotional stress and such) in Team Kurenai, if he replaced Shino (as much as I think Shino is a cool guy). Kiba would have served as a solid rival to keep Naruto motivated, even if Kiba isn't a transmigrant or whatever. Hinata, obviously, would have been supportive of Naruto, and being on a team with him might even have helped motivate her to become stronger and more confident early on.
Might have been an interesting manga in a different but fresh way if Naruto and Sasuke remained rivals, but on different teams.