As noted previously, run CAT5/6 everywhere. Everywhere is, each place where you need a light, each place where you have any kind of electrical outlet, each window and door. Run 2-4 CAT5 cables to every place where you think you already know you need 1. If feasible run an HDMI cable from your central wiring closet to the your intended TV place.
Did I mention to make sure to run enough cables
Yes, cables do cost money, but in the end of the day, putting the cables in now, will save you a lot and will later on greatly enhance the SWMBO / WAF factor.