post-credit scene of Norton's Hulk has Tony Stark meeting General Ross in a bar, mentioning that he'll help with the "Hulk problem," or something along those lines. Presumably an early idea was to have Hulk as more of an antagonist or something. This was all back in 2008 when the only Avengers business was the post-credit scene from Iron Man.
When actual plans were forming that didn't align with earlier ideas, they made this short clip called The Consultant with Coulson explaining: "oh, Tony wasn't serious. Secretly Ross wanted Abomination in The Avengers, and we didn't want that, so we sent Tony in to annoy him (

) into dropping that idea."
Also, originally The Hulk was responsible for finding Captain America. Banner went to kill himself on a glacier and hulked out, smashing it, revealing Captain's body.