Much to my chagrin, the role of another iconic brunette comic book character has been filled by a blond. Meet the new Wonder Woman:

Australian actress Teresa Palmer.
I gave Bryan Singer the benefit of the doubt when he cast Kate Bosworth as Lois Lane in Superman Returns, because I trust and love Singer, but it still didn't work for me. She has the acting down, but she's too frail and her hair was a mousy brown. I know it's just hair color, but we're talking comic books. Icons. Mary Jane was a redhead. Wonder Woman and Louis Lane were brunettes. Hair is important - Rogue from X-Men went through many alterations, but she always had the white streak in her hair. I'm stressing the word icons here, because that's what comic books create - the essential image of a character.
If you're going to make a movie about these icons, they better look the part more than anything. However, there is room for retooling (Singer made a good call on ditching the yellow/blue uniforms of the X-Men for the film)...AND an actor who didn't precisely fit the role has proven to make it work fantastically - Hugh Jackman is 6'2'' in real life and Logan/Wolverine is supposed to be short (like 5'6''), which he and Singer pulled off in the movie. [Sidenote: Jackman is coming back to fulfill the role of Wolverine in a movie just about the character, with Singer directing. FANX.]
I guess we'll just see how Ms. Palmer does.
Edit: after a bit more research, this is for the upcoming Justice League of America movie, and NOT the much-talked-about movie based solely on the character of Wonder Woman (still to be cast). Justice... will also be directed by the same guy who did Babe and Happy Feet. Therefore, this movie will probably suck anyway, whether or not Wonder Woman is portrayed by a fierce brunette. (Heyohhhh Lynda Carter!) Also, this movie comes out in 2010, so why do I give a fuck???
Okay, this is obviously a slow work day.
And...holy crap, I'm such a GEEK when it comes to this shit. My apologies.