A few routers can do this -- you'd have to look into the details of your particular router's feature set, as well as potential third-party firmware options for your router.
Or you could deploy another router or a PC-based software router to do this. There are even some add-on devices that can do this (but I haven't looked into them).
Here's a link with some options for routers. http://ask.metafilter.com/mefi/21629