Kristen Beth Williams. I happened, more by accident originally, see her in almost everything she's done - mostly Ensamble roles here in NY - but she almost gets a big understudy gig and while I haven't had the chance to see her go on as the lead in those, I have heard great things about it. She was in Promises (us Marge), Anything Goes (us Reno), Nice Work (us Duchess, Eileen & Jeanie) and Pippin (us Catherine)
I did see her as Dale Tremont in the London production of Top Hat, where I just thought she was a star! She was so good in that show and got great reviews (she replaced but because they replaced all leads at the same time they had a 2nd press night and round of reviews). And it baffles me that playing a lead in London apparently doesn't mean you have better chances to get cast in a semi-big role in NY... It makes me sad and hope she'll have her big NY break soon!