Run cat5/6 everywhere.
Good advice. The cable is cheap enough to get in during the initial construction phase.
It might not be something that everyone wants but if you have multiple desktop PCs, you'd much rather just have them with a hard connection than using wireless.
On that note, you might want to look at where you'll want to place your router (I would wall mount it somewhere centrally located) and have a connection set up there.
If you like to cook and entertain a lot you might want to consider a double oven and/or warming drawer