I actually thought it was a joke when I first heard, I couldn't believe it. While not an astounding actor, he was pretty good (just some bad choices of movies, really). Really thought Dark Knight would be a high point of his career; now that's basically garuanteed. I didn't really peg him as someone who would do this, either, and 28 is just too young to go. I think it's funny that some people around here assume that because they're celebrities with money, that they can't possibly have stress or issues they fight with like normal people. Not that I agree with suicide, because I don't, but celebrities have to deal with the stress of the crazed media on a regular basis.
On the topic of Dark Knight, apparently he was to have a fairly substantial role in the third film though, so this could cause a problem there.
RIP Heath.