A couple of things he mentions in this interview that I didn't know, and I'm assuming some of you didn't know as well, are that, first, Don Cheadle was actually the Studio's first choice to play the character all along, from the very first Iron Man movie with Robert Downey Jr; not Terrence Howard. But, as Terrence says to Sway below, his agent was able to get him the role, beating out Cheadle.
So, in a way, it's kind of karma isn't it, that Cheadle ended up in Iron Man 2, and will be in the upcoming 3rd movie as well.
Secondly, he said that he had a 3-picture deal with the studio to make 3 Iron Man films, and he was apparently supposed to make $8 million on the second film (he says he got paid about $4 1/2 million for the first film). But, he (or rather, his attorneys, manager, or somebody) didn't do their job adequately, because, it turned out that, despite the signed 3-picture deal, the studio gave itself an out in the contract, that would allow them to replace Howard if they wanted to, which he says in the interview below that he didn't know, or that he forgot.
So, there he was expecting an $8 million payday for Iron Man 2, but got suddenly hit over the head with news that they didn't want to pay him that money, especially if they could get Cheadle for a lot cheaper at that point, and instead of the expected $8 million, they offered him even less (a lot less) than what they paid him for the first film, and certainly a lot less than what he was expecting - they offered him $1 million for Iron Man 2.
Obviously, he passed, and moved on, and Cheadle got the part. I'm assuming he also got paid $1 million.
They go into a bit more detail on the entire situation, so it's worth a listen. But I love learning about these back-room studio dealings. It's all very fascinating to me.