The Incredible Hulk
Avengers Contributions: Hulk origin / Introduction of "Smart" Hulk / First Marvel Movie Crossover / *Captain America Introduction
Like Iron Man, The Incredible Hulk was an early addition to the Marvel movie universe - before Marvel Studios president Kevin Feige and the other execs necessarily had a clear sign of whether or not The Avengers was going to be a feasible endeavor. That initial uncertainty meant that Marvel had to again create a self-contained film, with only loose ties to a larger mythos. Having received the Hulk property rights back from Universal, Marvel Studios had the equally daunting task of having to wipe away the bad taste left in moviegoers' mouths after Ang Lee's lackluster 2003 film, Hulk.
Incredible Hulk wasn't quite the runaway smash that Iron Man was; in fact, the reboot made pretty much the same profit margin as Lee's film did ($263 million on a $150 million budget). However, even though The Hulk didn't smash the box office his second time out, Louis Leterrier's retooled version of the jade giant did score major points with Marvel's primary base (fanboys), and offered more irrefutable proof that Marvel could adapt its characters for the screen better than some third-party studio ever could.
A mid-credits scene featuring Robert Downey Jr. as Tony Stark sent fanboys into the geek stratosphere by giving us the first official Marvel movie crossover, while other elements of the story (Bruce Banner's research into the super-soldier project and the subsequent creation of The Abomination) only added to the fun by hinting at a larger universe waiting in the wings to be explored.
(*An alternate opening to Incredible Hulk also features a sequence of Bruce Banner in the Arctic attempting to kill himself, but instead triggering The Hulk (remember that anecdote from Avengers?). The enraged Hulk smashes a glacier, inadvertently breaking open the ice containing Captain America. Go HERE for a look at that moment.)
With two (relative) successes under its belt, Marvel Studios had all the reason it needed to push on down the road towards The Avengers.
Verdict: While it's only so-so as a standalone film, Incredible Hulk implemented its shared universe elements without sacrificing its self-contained story.