Iron Man (2008)
The first -- and, so far, still the strongest -- Marvel Studios feature offers three Avengers-related tie-ins. First, Captain America's famous shield can be spotted lying on the ground in Stark's workshop, a tease that director Jon Favreau credits to a special-effects artist at Industrial Light & Magic who added it during post-production. Secondly, the movie introduces the top-secret government agency S.H.I.E.L.D., which acts as a recruiter/liaison for the supergroup. Then, in a post-closing credits sequence, viewers are treated to their first glimpse of Sam Jackson as S.H.I.E.L.D. head Nick Fury, who confronts Tony Stark in his home and informs him that he's just "become part of a bigger universe." He then utters the fateful words that sent shivers through the hearts of fanboys around the world: "I'm here to talk to you about the Avenger Initiative." And with that, we were off and running. (Actually, there is one other significant cameo we should note: Tony's A.I.-enhanced butler JARVIS, voiced by Paul Bettany, is a nod to Edwin Jarvis, the Alfred Pennyworth-style butler that ran the grand Stark abode -- which became the Avengers Mansion -- in the comics.)

The Incredible Hulk(2008)
Though not a Marvel Studios production (Universal financed and distributed this reboot of Ang Lee's controversial 2003 version of the not-so-jolly green giant), The Incredible Hulk does feature a quick appearance by Tony Stark, who shows up for a chat with the military dude on the Hulk's trail. And in a deleted scene that's included on the DVD, the frozen body of Captain America can be seen buried beneath the ice at the Arctic Circle, where the Hulk's human alter ego Bruce Banner has gone to try and find some peace.

Iron Man 2
The most obvious Easter Egg is Thor's hammer Mjölnir, which is glimpsed in the Arizona desert at the end of the movie. It's the first hint that intergalactic travel between our world and distant, deep-space realms is possible -- a plot point that will likely play a big role in The Avengers. Iron Man 2 also introduces Johansson's Black Widow character, brings Fury back for a longer sequence and gives Cap's shield a more prominent viewing, directly tying its creation to Tony's father, Howard Stark, who will be a supporting character in the Captain America movie. More eagle-eyed viewers will notice that a news report depicting a battle between the Hulk and a squadron of soldiers is playing on a television in the background of one scene. (While not specifically Avengers related, another background prop is a world map that highlights Wakanda, the African country that's home to Marvel's first black superhero, the Black Panther.)

Thor
The key character introductions in this fantasy-laced superhero outing are the Norse God's prankster step-brother and chief nemesis Loki and Renner's Hawkeye, both of whom will be featured in The Avengers... on opposite sides, of course. And despite the fact that he's fairly useless for much of the movie, scientist Erik Selvig (played by Stellan Skarsgard) does get to deliver two prominent Avenger-related references, offhandedly mentioning a colleague he knew that was an expert in gamma radiation (that would be the good Dr. Banner, of course) and meeting up with Fury for a private viewing of a strange mystical cube that possesses cosmic powers. (This scene also suggests that Loki is using Selvig as a way to monitor what's going on Earthside, which explains why Skarsgard will be back for The Avengers as well.) Stark's name is also bandied about by a S.H.I.E.L.D. operative (Clark Gregg's Agent Coulson, who is another staple of the Marvel cinematic universe ) when he catches a glimpse of the Asgardian iron giant known as the Destroyer.

Captain America: The First Avenger
We haven't seen the movie yet, but it's already known that the aforementioned Cosmic Cube appears again here as the object that the film's chief villain -- Johann Schmidt a.k.a. the Red Skull (Hugo Weaving) -- is eager to get his hands on. We'll probably also get another Nick Fury cameo, perhaps one that delves into the Fury family's lineage since the movie also includes the Howling Commandos, the World War II-outfit that Fury headed up in the pages of the comic book. Is Nick older than we think or did Grandpa Fury oversee the Commandos? Finally, The First Avenger will directly set up The Avengers by bringing Cap out of the past and into the present day and treating audiences to a brief trailer (one that's already leaked online) for the film, due out May 4, 2012. C'mon Fandango -- let's get those advanced tickets online already.

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