Most Harry Potter fans have been theorizing and waiting to see who they will cast for some of the bigger parts in the movie for Harry Potter and the Order of the Phoenix. According to Wizard News, Imelda Staunton (of Vera Drake fame) has been cast as Dorothy Umbridge. I can't think of another British actress more perfect for the part.
Also, it seems the production team has been scouring schools around the UK looking for the perfect Luna Lovegood. Some teenaged Brit is going to be very, very happy!
I'm still wondering if they will bring in a big name to play Bellatrix Lestrange. A rumor was out in August that UK actress Helen McCrory would play her, but nothing has been confirmed as of yet.
What about Tonks? Hopefully her part won't be written out of the screenplay.