Yes it is.
Each of the Marvel films starting from Ironman (The Incredible Hulk, Ironman 2, Thor, Captain America) all had post-credit scenes that built up to the Avengers movie.
Post-Credit Scenes
-Ironman: introduced Nick Fury and the first word of an "Avenger Initiative"
-The Incredible Hulk: Tony Stark made a cameo and said they were recruiting for "a team"
-Ironman 2: showed Mjolnir at the end of the film
-Thor: showed that Loki survived and introduced the Cosmic Cube
-Captain America: showed the first Avengers teaser
The Avengers is going to include Ironman, Captain America, The Hulk, Thor, Hawkeye, and Black Widow. They'll be up against Loki and the Skrulls if I'm not mistaken.
The Avengers trailer:
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