-Firewall
-WEP
-Turn off Broadcasting of your network Name if it's your wireless service
-USE MAC address filtering. Basically only allows the computers you specify to use your service.
Still holes in wireless...but those are the best things you can do...and you should use all of them. It still won't be completely secure...but those 4 things I believe are about as secure as you can make wireless at a 'home consumer' level.