If you really want to make things a pita... turn off the SSID broadcast and if your router supports it use the MAC address filtering to only allow the MAC's that you have on the list to have access...

Also a note to those that are not as tech savvy.. If you have devices that are older, or that aren't a pc like a game console, WPA might not work for your network because some of the stuff out there does not support WPA...

and lastly... no matter how secure you make WIFI.. if someone is that bored or that serious about getting on you network there is always a way... but in most of our cases it not worth it for someone to try...