PayPal seems to be one service that a lot of designers use for UI design or concept redesigns. I quite like that because it’s a finance application. It’s in a way not towards social/user generated content where it’s all about style or beauty. It’s about money, balance, transfers and stuff like that.
Filippos Protogeridis shared a good one on his Behance profile. It has a simple and elegant UI design, but doesn’t shy away from going more more image heavy on promo page for example. We like this concept much more than the official and current design.