Neat little app that let's you pick out a device on the network and kill it, or kill them all. It doesn't kill the wifi for a victim, instead it rejects all the traffic, blocking access to the webs.
Best thing is that you can redirect the victim to any IP that you set in settings.
I just tried it on my "HTC Wildfire" with "Cyanogenmod 7" with me as the victim, redirecting all the traffic to 188.8.131.52 (meatspin IP) on port 80 and it worked really great. Of course it blocks the traffic as long as you keep the app running or select not to block the victim anymore.
Also I think you should have Busybox installed, since it uses IPTABLES - the powerful Linux firewall - to these things, and of course you need a rooted phone. But I don't know what phones support this, so try and report!