The Avengers: On rarer occasions Tony Stark (Iron Man) / Steve Rogers (Captain America) /Thor or Tony/Steve/Pepper Potts or the "Cold Irony" ship (Tony/Steve/Tony's Sentient Armor, because Iron + Tony = "Irony" and Steve was frozen). Or just really Tony/Steve/? (there have been Spider-Man, War Machine or Jan Van Dyne in the "?" place).
Danny Rand/Misty Knight/Luke Cage are very close too each other. Danny/Misty is canon, and when Luke had a baby, he named her after Daniel. Aww.
Danny Rand/Jessica Jones/Luke Cage seems to be pretty popular as well.
Some people have all four together, Sometimes with Colleen Wing coming for a visit.
Runaways: Some fans like Nico/Karolina/Xavin. The possibility was even brought up in the comic, when Xavin impersonated Nico and tried to seduce Karolina, but Karolina was too weirded out for anything to come of it.
Spider-Man: Spidey/Mary Jane/Black Cat or Gwen (The first one tend to be more popular). Sometime, it's a foursome. Weirdly enough, Ultimate Spider-Man implies that Gwen was trying to initiate Peter/MJ/Gwen, since in a line she mentions that she crushes more on her close friend MJ than on Peter.
