Tomorrow Belongs to Me by
valtyr is basically exactly what I want The Avengers movie next year to be in my slashiest, wildest fantasies. The characterizations are spot-on, and the story is incredible, but the best part is it's Steve/Tony, and I'm a huge fan of that pairing (and, well, anything with Tony being Tony and Steve rolling his eyes and putting up with him). Read this if you want some lengthy awesomeness!
(Note: even the summary is perfect!
Summary: Steve wakes up in the 21st Century. He doesn't think much of it, and it's dubious about him. He meets a Norse God, joins a superhero team, and feels terribly awkward about the whole monument at Arlington he's rendered obsolete by not being dead. Meanwhile, Tony is trying to make his mark on history by being the man who finally drove Nick Fury over the edge.)
Enjoy! And make sure to check out a few of valtyr's other stories too!