As of The Avengers, the six heroes who form said Avengers are: Steve Rodgers as Captain America (played by Chris Evans); Tony Stark as Iron Man (played by Robert Downey Jr); Bruce Banner as The Incredible Hulk (played by Edward Norton in 2008 and Mark Ruffalo in The Avengers); Thor Odinsson as The Mighty Thor (played by Chris Hemsworth); Natasha Romanov as Black Widow (played by Scarlet Johansson); and Clint Barton as Hawkeye (played by Jeremy Renner).
There's also Samuel L Jackson as Samuel L Jackson Nick Fury, Clark Gregg as Agent Phil Coulson and Cobie Smulders as Maria Hill.
All of these people are awesome.
Plot summaries of movies below, for people who haven't seen them (to whom I say: WHAT IS WRONG WITH YOU?! Go watch them!). Everyone else, feel free to squeal away about how awesome The Avengers was, though it might be polite to keep spoilery squeeing and discussion under spoiler tabs until about May 7th, when it'll have been out in America for a few days.
[spoiler=The Incredible Hulk]

Starring Edward Norton as the titular Hulk.
The latest retelling of Dr Bruce Banner's life-changing experiments in gamma radiation, and along with the first Iron Man movie the kickstart of the Marvel Cinematic Universe. The movie actually begins about five years after the accident which created the Hulk, probably on the basis that everyone knows about it already. Bruce Banner is trying to keep his head (and temper) down in the backwaters of the world, but a spilled drop of his gamma-irradiated blood is all it takes for General Russo and Emil Blonsky to track him down.
Needless to say, Banner eventually loses his temper, and things get smashed.[/spoiler]
[spoiler=Iron Man]

Starring Robert Downey Jr as Tony Stark.
Tony Stark is a billionaire, a playboy, and a genius, making his billions creating and selling ever more powerful weapons to the US army- until a terrorist attack in Afghanistan changes his life by nearly ending it. Tony escapes the terrorists that captured him by telling him that he'll build the missile that they want and using the weapon parts that they bring him to create a suit of armour and blow up their base (seriously, how did they think that would end well for them?)
Tony now has a miniature ark reactor in his chest to keep a cluster of shrapnel from digging into his heart, and has realized the true destruction caused by his profession. But he has a plan to set it right. If only he had more money than Bruce Wayne and a powerful but portable power source to work with...
The first movie came out in 2008 and started off the Marvel Cinematic Universe and was followed by Iron Man 2 in 2010, where Tony has to deal with the grudge-bearing Ivan Vanko, a burgeoning relationship with Pepper Potts (Gwenyth Paltrow), SHIELD, and his own mortality.[/spoiler]
[spoiler=Thor]

Starring Chris Hemsworth as Thor Odinsson and Tom Hiddleston as Loki.
Astrophysicist Jane Foster (Natalie Portman) accidentally runs over a man while following a bizarre cloud formation and aurora- both of which appear to be connected to other worlds, and to the strange man who claims to be the Thunder God Thor...
Thor himself must discover what qualities a true king needs that he is lacking, while dealing with the threat of Jotunheim- and a shadowy danger from within his nearest and dearest.
This film sets up the major antagonist of The Avengers, the very reason that the Avengers themselves were formed.[/spoiler]
[spoiler=Captain America]

Starring Chris Evans as Captain America.
Steve Rodgers is a sickly, puny guy that the army repeatedly deems unfit for service in WWII, but Dr Erskine thinks that he has the heart and courage fitting for his supersoldier project- a serum that will turn even the scrawniest physical specimen, like Steve, into a nearly immortal superhero. It also enhances everything inside of a person... so while a good man like Steve is turned into the first superhero, the serum's previous test subject, Nazi scientist Johann Schmidt (Hugo Weaving) is ready to match him as its first inhuman supervillian. The two scientifically-enhanced soldiers clash over the Cosmic Cube, a small chunk of unlimited energy that could give Schmidt the power to control the world... or destroy it.
The Cosmic Cube is an extremely important plot point to The Avengers, so keep an eye on it. The movie explains how Steve ended up being frozen in ice for seventy years, allowing him to fight alongside the other heroes against a present-day crisis...[/spoiler]
[spoiler=The Avengers]

The big one... so far. The one that the other five have been building up to. Earth is threatened by an utterly deranged Loki, wielding the Cosmic Cube and controlling the armies of the Chitauri. The most remarkable people on earth must come together in order to save it... so long as they can stop snarking at each other, fighting each other, and generally get along for about five minutes straight...
As someone who has seen it twice; yes, it IS worth all that hype.[/spoiler]
Iron Man 3 is set to be released on May 3, 2013. Thor 2 is set for November 15, 2013. Captain America 2 is set for April 4, 2014, and an Ant-Man movie is planned for some time in 2014. A Black Widow movie is also being discussed.
So... below is my squeeing rant about how amazing The Avengers was. Feel free to add your own thoughts, chat about the upcoming movies, or whatever about the Marvel Cinematic Universe

[spoiler]
Natasha Romanov is tied to a chair, surrounded by three large men with torture instruments, and is given a phone with Coulson on the other end and asks him to hold. Three minutes of agony later, the Black Widow stops to pick up her shoes on the way out.
My friends singing “Snape, Snape, Sev-er-us Snape!â€