Innovative Web UIs

I love the use of pop-up definitions and readings on this site (warning: great functionality, but fugly design.)

Rikai allows you to paste in Japanese or Chinese website URLs and get instant mouse over pop-ups with readings and definitions for all the kanji (ideograms.) For someone studying Japanese or Chinese, this is an invaluable tool. It allows you to read websites such as asahi.com before you know the 3000 or so characters necessary to read a typical newspaper. You simply move your mouse along the lines as you read.

Note: I know this site has been around for a while, but it is still not as well known as I would expect.