The fact that JKR killed Sirius pissed me off really seriously (haha!! Serious! Sirius! get it?! yeah I know that was dumb) Furthermore, I don't see how it was at all relevant to the development of the plot. If she thinks that she can attract more readers or make it seem more "dramatic" by killing off the most worthwhile characters, she is very, very wrong. It is possible to make a story better by having a character die (for example in LotR when Boromir died--that was the cause of the whole Faramir/Denethor thing in RotK which was sad but at the same time quite interesting to watch) but in this case there is NO POSSIBLE WAY it could have made it better in any way. Personaly, I liked Sirius more than Harry, Hermione, Ron, and all the other main characters. And yes, by that I do mean that she may as well have killed Harry. (don't hurt me too badly for saying that) The books will simply not be as good for me from now on.
I think Johnny Depp would be a good actor to play Sirius... Some other ideas: the guy who played Dorian Gray in "League of Extraordinary Gentlemen," Viggo Mortensen, Hugo Weaving, and Keanu Reeves....
ps Pippin rules!!!! His little song in RotK was really well done and that was so cool how they showed scenes of Denethor pigging out and Faramir getting "killed" by the orcs.. It really showed how uncaring and mean Denethor was