Are there any wireless routers that allow bandwidth monitoring and throttling?
I don't know the specifics of each, but DD-WRT and Tomato are two firmware options I've heard a lot about; they might be able to do something like that.
tomato and ddwrt are great and allow for monitoring and quality of service for prioritizing packets but they do not allow for throttling. that is, you cannot set maximum available bandwidth for a segment of the network.
if you want to do limit bandwidth, you have to pay for a special version of dd-wrt. see http://www.dd-wrt.com/wiki/index.php/What_is_DD-WRT%3F#Special_Versions for more.