Hawkeye/Natasha. Bruce Banner/Natasha. And here I am about to sally forth with my own 'ship manifesto. I know what it looks like: We're gleefully, even shamelessly, pairing Black Widow up with everything in pants because she's the only female member of the movieverse Avengers. Let me get three things out of the way. 1.) Despite the off-color comments some castmembers have made, it's safe to say the Avenger most likely to bed-hop is international playboy Tony Stark. Remember the stripper-pole-sex-plane? Oh, the exploits JARVIS must have seen. 2.) My chosen partner isn't even an Avenger. So there. 3.) Natasha Romanoff is a total badass and a strong character in her own right and she doesn't need a love interest to be validated.
But when you're this amazing, why shouldn't you have someone to cuddle up with at night? Or at least someone to clean your guns with and reminisce with about the old days when you used to be an evil secret agent. Nat is awesome. She should get it.