Chris O'Donnell just seems like he should be best friends with the two Coreys. 'Nuff said.
I'm just against Robin in the films for one reason only. It distracts from the dynamic of Batman, his personal life as Bruce Wayne, and the villian (which includes the relationship dynamic between the three arcs). Shoving Robin into the mix works well in the comics as a segue, or even relative to the arc, but that can be drawn out for infinitely more time and with more depth and complexity than a film can provide. Sticking the character into the films serves to limit the time and depth of each individual character, as it becomes a muddy, rushed mess. Personally, I think it's just a poor idea overall.
To give a brief example of what I mean, think of the X-Men films. Other than Wolverine (who really shouldn't have been the focal point of any film other than the current one), there is no character depth explored fully. No shaping, no full backstory, just some vague references and minuscule flashbacks that (other than the people into comics.. you know, geeks, nerds, fanboys, and whatever other words we could use..) serve the character nothing, as if we should just accept their being and existence as the whole story, when it isn't and shouldn't be.
Even Nicholson's Joker had a backstory. Ledger's Joker had no backstory... and that was the point. The whole idea was that they knew nothing. The premise is brilliant, ties into the comics well, and leaves the viewer practically begging for more.
To reply... Jedd, I don't think of Pitt as a character actor in the same way I don't think of Johnny Depp as a character actor, or Edward Norton for that matter. I find myself consistently amazed at the variety of roles that he takes on. Is he a draw for the ladies? Absolutely... but even the most squeamish of girly-girls still loved SE7EN... "Aww... What's in the box?!?!???" Fight Club is a movie that women are severely divided on (those that saw it are also divided over the violence versus the topless men, then there's the "I won't see it because it's about fighting" crowd, all of which obviously have no clue what the movie is actually about).
That actually leads me to thinking more about Keanu Reeves. I still say no thanks. I'd rather watch Al Pacino (who has become a character actor by the very definition) play Batman. I'd rather watch Peter Griffin play Batman. And speaking of animated series... I think the perfect choice for a Joker in any subsequent films would actually be Mark Hamill. Think about it... the makeup would hide his age (face it, he's got a few wrinkles). He's got the best (wow, my original word got changed to "gorram") Joker laugh ever (beats Nicholson by a mile), and you could play off the changes due to his captivity (Arkham Asylum would come back into the picture, thus contributing to the "rehab" efforts and changes). Maybe he disfigured himself a little further, maybe he got into the medicine cabinet... but I think Hamill could follow up Ledger with some justice to the style of character needed in the Nolan films. He's got the voice, he's got the mean streak (like just about killing Vader before he decides not to give in to the hate), and considering the costume and makeup work, I think the differences would be negligible.
Oh... and that new movie with Ben Affleck (and Russell "The Cellphone" Crowe)... don't see it. Fair warning. It will be terrible.