I don’t believe there’s anything in the books that suggests Angua is busty. In fact she should look kind of lean, muscular, and wolflike. Because Keira has played several quite tough fit characters, that’s why I figure she’d be good. And she’s a Brit with that sophistication that could put her in a noble Uberwaldian family.
But there could be better choices, I suppose.
Actually, in Men at Arms (where Angua is introduced), Pratchett says:
Which, to me, suggests that she is very busty. The cover artwork appears to back me up on this one as well. Link
Paul Gross as Carrot.
Janet Henfrey as Granny Weatherwax. Dawn French as Sybil Ramkin. Kathy Bates could do Nanny Ogg with a bit of makeup. KellyM suggested Debra Messing as Magrat.
Tawny Kitaen would make a good Angua.
Diana Rigg for Granny Weatherwax.
