In the spirit of Ian’s post about responsive web design and the discussion ensued from it, here is a collection of examples of said practice and technique (not constrained to WordPress sites). Several good designs on display there.
Mediaqueri.es, a collection of responsive web designs
ThemeShaper 
I like http://webdesignerwall.com/, also Nick wrote really good post about blog redesign
Nick La’s responsive layout is super-clever. I love how the post thumbnail interacts with the comments icon at the smallest screen size. And everything else about it for that matter. 🙂