I found this site a few weeks ago and I can't wait to splurge on something. I haven't bought anything from them so this is not an endorsement. What first grabbed me was some of the new ibm X-10 technology, really neat stuff and cheap.
I saw they had some stuff for where all your wires come together in the basement. They have some wiring panels and connectors and outlet boxes etc as kits. Here are some links.
I haven't thought this far ahead with my addition. Maybe someday I'll get one of these.
http://www.smarthome.com/8632.html $500 kit with everything you need (except the wire) for video, audio, phone and computer wiring. Pretty neat!
http://www.smarthome.com/8680.html even cooler (and more expensive) for complete future expandability.