Good answer it is always a problem with urban areas when a lot of wirless networks spring up all using channel 6, some manufacturers have recognised this failing and set the deafult to either 11 or 1 but changing it is a simple matter.
Also the setting for 'b' and 'g' modes should be looked at, By default these are normally set too accept connections on either 'b' 11mbs and 'g' 54 mbs, Ok under normal circumstances but if yor connecting equipment is all of te 'g' type simply setting the connection to accept only 'g' hardware will exclude a lot of extranious connection attempts.
Unchecking the 'Broadcast SSID' is also good pratice, as if your network is not broadcasting to the world who and what it is there is less chance of other wireless equipment other than your own trying to log on.
Finally the use of the Access listing, or MAC filtering is also a very good method of denying access to your network, nothing to do with MAC computers here, Media Access Control, something that applies to every computer and wirelss capable device is that it has a unique MAC address associated with it, something you can use in your router interface to allow only those computers and devices access too the network, in short if it's not listed it cannot connect, Can be spoofed, but to do it you would need to be very computer aware and have a very good reason, not in the realms of most users.