I dont think big tits are the be all and end all of Catwoman.
I think what they need is someone who can act, is sexy but can also play a tough character.
I dont think anyone would be surprised that my first choice would be Charlize Theron, but I can think of several other actresses who might be able to play a role like this:

Mila Jovovich
Christina Ricci
Anne Hathaway
Evangaline Lily
Eliza Dushka
Ali Larter
Jennifer Connelly
Scarlett Johansen

Snarf is shit. His death will be rejoiced!