I'll be adding more recs whenever possible, but for now...
Freezer Burn: gen, focusing on Captain America, WIP
A really insightful and entertaining read on how our favorite Capsicle adjusts to life in the 21st century while fighting enemies from the 20th. The Avengers all make an appearance and they are solid and realistic characters. But first and foremost, you get an in-depth look at how Steve Rogers tries to function as both Captain America and just plain ol' Steve without compromising either.
The Scientific Method: gen, humor
Tony and Bruce discover Steve can't get drunk. They decide to solve this problem using science, methodically. Chaos ensues.
Reflections: gen, post IM2
Natasha and Pepper have a short but revealing discussion regarding Tony's predicament with SHIELD, and how close he came to dying, and not just because of the palladium poisoning.
Melting Pot: het, post Avengers
Has my favorite original female character. Beautifully written and well explored about what happens when the American Icon falls in love with a Muslim woman. Also, has the worst marriage proposal by an Avenger in fanfiction: barring those including death, Armageddon, and Roombas.
The Long Dark Night That Follows: slash, post Avengers
It's easy to forget in the chaos of super-soldier, Iron Man, and a demi-god that Hawkeye is, at the end of the day, a man. So, what happens when that man becomes superficial (or believes he's become superficial)? The slash is at the end, good writing from the first word to the last punctuation.
Culture and Other Balls of Twine: het, humor
One of my favorite gen stories in AO3. And the writer should be familiar to SPN fans. It's basically Avengers take a Road Trip because Tony's a spaz and Bruce can't say no, though he does make hearty attempts at it. Also, Selvig and Jane Foster make kids cry. The ending is a hoot!
A Different Glow For Every Window: het, introspective
Natasha knows the difference between assassin and hero. What she is slow to realize is that sometimes you can be both.
Irnan's story list ...
Just click and sacrifice a night or two to good fanfiction. Okay? Okay!
She Blinded Me with Political Science: het, humor
Darcy Lewis (the minor character who tasered Thor) is why fanfiction exists and should continue to exist. In this story she basically tries to help Avengers regain their popularity after Midtown was flattened to the sewer lines. Oh sure, these characters saved the day, but who are they? Should humans trust them? Should anyone have that much power? And, most importantly, who's going to pay for the cleanup? As you can see she's got a long, long road ahead, especially since she wants Bruce Banner to allow Hulk to make a public appearance: in an enclosed space, filled with voracious media.
Kellifer’s stories: gen, het, slash, humor, Dalek.
Probably everyone knows this author, and how good her SPN stories are. Well, everything carried over to the Avengers and with interest!
Imprint: gen
Steve Rogers slowly comes to terms with who he is relative to the 21st century. Of course, the others have to, also. Love how Steve Rogers is in this story: vulnerable, fierce, and paternal. You could definitely see why the Howling Commandos would kill and die for him.
I … just go read, okay?: gen, slash, het, humor
I’m usually a stickler for canon, but then there are times I would happily go off the mountain, and stories like these are why. And though it is OC (the writer admits as much) the humor attributed to the characters is dead-on, especially Natasha. Also, SHIELD air ducts ate Clint, once.
No, that’s not a typo.
Jarvis Series:
Hard to quantify this one but it is a fantastic read on how the Avengers react when they realize that Jarvis is not just playing Jeeves to Tony’s Wooster. And that the AI can and will make life or death decisions on his own, because Tony has given him the freedom to do just that.
Strobelight Serenade: humor, slash(?)
Tony discovers Captain America never went to prom. This has to be corrected.
Immediately.
Unfortunately, he decides to do so with the Macarena. Surprisingly, Natasha doesn’t kill him when he suggests it. I know this sounds about as plausible as waking up to three suns, but it really, really isn’t.
The Only John Wayne Left in This Town: humor, het
“Two roads diverge on an Iowa highway overpass, and Clint, being a stubborn little fuck, takes both.”
Clint Barton is Hawkeye. He is also Dirk Hawksley, the man who is going to save country music. Sometimes being a stubborn fuck is not a good thing. But, it could also lead to whole lot of interesting scenarios.
Gyzym also wrote
We Were Emergencies: hands down my favorite story in the Avengers fandom. It is ferocious, heartfelt, and heartbreaking: A true hallmark of great writing.