I recently discovered this Yobo online music streaming service for Chinese songs. You can get a free account and start listening to many Mandarin songs online. It works just like Pandora.
It’s a great way to learn Mandarin!!! ;)
http://www.yobo.com/ Updated (Dec 24th, 2012): Apparently Yobo is down indefinitely, but check out this new service: http://birdchan.com/home/2012/12/24/chinese-pandora-2/