1) get decent router that supports DD-WRT
2) Load DD-WRT firmware on said router
3) Under the restrictions section of the dd-wrt control panel you can disable internet connection by MAC address, ip, and you can even restrict times of the day the client can browse the net. So, lets say you have a kid, and want the internet to shut down at 8pm every night, you can do that by configuring it in your router.
check this out for a full list of compatible routers
www.dd-wrt.com