Boden is the best at this, I think. Modcloth lists some measurements for most of their garments, although it's not particularly complete (for dresses, they usually list just the length).
I know Michael mentioned in the comments on one of Angie's Karen Kane post that they were planning on doing this for the Karen Kane website in the future, but that it was taking a while to get measurements for each size of each item.
I really do wish more websites did this, especially if they don't offer free shipping/returns. I am MUCH more likely to order something if I know I will actually be able to zip it up!