WARNING: Major "Iron Man" spoiler follows (though how much longer this can remain a surprise is very much in doubt) so be warned.
So, "Iron Man" sold in the area of $100 Million dollars in tickets, exceeding it's boxoffice expectations by about 30-40 mil and basically putting a big "Take Us Seriously" sign on the new Marvel Studios. That's the business news. For fans, the biggest POSSIBLE news came after the credits, when those prescient enough to sit through the credits saw an extra scene in which Samuel L. Jackson - playing the "Ultimate Marvel" version of Nick Fury, Director of S.H.I.E.L.D., shows up at Tony Stark's house to talk to him about something called "THE AVENGERS INITIATIVE."
For those for whom that doesn't have much meaning, "The Avengers" are Marvel's premier superhero team; boasting a rotating roster of members that usually starts out including Iron Man, Captain America, Thor, Ant-Man/Giant-Man and The Incredible Hulk. You may notice that that list ALSO neatly comprises the roster of Marvel characters who have films either in release or production under the singular "Marvel Studios" banner. So the question is, is this just MASSIVE optimism on Marvel's part, or are this summer's "Iron Man" and "Hulk" movies part of a long-term plan.
As of today, Marvel has an answer:
Short version: "Iron Man 2" and "Thor" in 2010, followed by "The First Avenger: Captain America" and 2011 and "The Avengers" after that. Regarding the titling of those last two: In general Marvel continuity, Captain America is a WWII-era superhero who finds himself trapped in suspended animation just before the end of the war and is later revived in modern times, where he joins and becomes de-facto field leader of The Avengers; so the titling there could concievably indicate that Cap would debut in a WWII-set film of his own and then turn up time-displaced in the "Avengers" movie... which is almost too cool to contemplate.