Both Mark R. and David G. have mentioned Cisco routers as being devices that 
can serve your needs, but they also suggest that these can be quite 
expensive.  I just wanted to add that it looks to me like Cisco has added a 
"Guest" account feature to their home user routers, such as the Linksys 
E-1200.  I haven't used one of these routers to explore it in more detail, 
but apparently the router does provide a segregated wireless network, 
separate from the main LAN that your computers would be connected together 
on.  You give your guests a different wireless access password than the one 
that you would use yourself on the home network.

http://homestore.cisco.com/en-us/Routers/Linksys-E1200-WirelessN-Router_stcVVproductId129966524VVviewprod.htm

http://www6.nohold.net/Cisco2/ukp.aspx?pid=80&app=vw&vw=1&login=1&json=1&docid=c3e42afc03994df5bb6bc531b42e9201_21461.xml

I hope this is helpful.

John Sproule

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