I was actually referring to Hawkeye (archer) and Black Widow (chick) but the comparison between Batman and Tony Stark works better.
I come from a comic perspective in which, following Avengers storylines, both characters are fairly strongly represented, however if someone has only watched the Marvel films then these two characters are probably going to seem tacked on, however I think the film will really show these characters off as being fairly integral, they just may not be as flash bang as the others
Hawkeye has a 'superhuman' sense of accuracy (often goes against Bullseye, bad guy from Daredevil movie played by Colin Farrell) and shoots a variety of modified arrows (shoot out nets, explosive head, electric charge, used to hold rople line) but acts as support to the other superheroes. He can be very stealth, is a bit of a commando and often is used in the more low key battles that don't need to be hulked.
Black Widow is like covert ops special agent. In the comics you never really know who's side she is on at any particular time, has little poison pellets in her wrist band (poison like a Black Widow) and is very good at infiltration. We know Loki is in the film, assuming there are some more human bad guys or superhuman bad guys, these two will both be involved in the fighting. They've both (in the comics) assisted to take out Hulk and various other oppoenents.
Thanks for the support Cas