What are the most interesting / unusual design elements used on websites that you have seen?

I am leading a team to build a website for a client. The client is a company producing games, toys and widgets. They have specifically asked for at least 2 design features on the site which are intelligent, interesting and unu开发者_开发技巧sual! (I am quoting the specs I got)

Further, they do not want any Flash - loads of JS are OK though.

I thought I would ask the SO community for their opinion. So, what are some of the most interesting / unusual design elements that you have seen or used yourself?

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This site has one of the more interesting gimmicks I've seen, and they appear to do it with script only. Scroll down, and you can see the images on the right stay in place relative to your browser, but different sections of the images are shown as you scroll. Hard to describe, but cool.

http://welbog.homeip.net/