There's a place in the Yangpu district of Shanghai, to the northeast, that has a massive park (link below) with facilities for those who like to skateboard, stunt bicycling and in-line skating, though honestly I would hardly consider that extreme sports.

I think there may even have been a paragliding competition held in Linzhou last year.

Beijing has lots of bungee jumping sites (2 links attached). You can also go rock climbing in Yangshuo, or you could go paragliding in Guangzhou (http://www.glideclub.com/main/home/main.php).

I find crossing the street in Guangzhou pretty intense and extreme!!

You can come here to Xiamen and learn kite boarding, assuming you haven't. It can be extreme sometimes with a BIG wind. Also the are some glaciers in North Western Yunnan where you could earn some turns (if you brought our own skis)...