I'm most looking forward to Ruth Madeley's character. I know that she isn't playing Hebe but it'll be so fun to see her together with Mel on the TV. Water Worlds are the main reason why I got back into Doctor Who a few months ago. Speaking of which, if anyone hasn't heard the Big Finish boxsets with 6th Doctor, Mel, Hebe and friends old and new I strongly reccomend them.
Other than her I'm really looking forward to Indira Varma's character. What else can I say other than I love Torchwood and Suzie.