I'm 100% in agreement with Rizla here.
But a decent gig switch that has some of the 'green power management' stuff inside. It turns off power to ports when not in use. I've got a 24 port managed switch and it's a beast on power use. Remember this is going to be on 24/7 pretty much and power isn't getting cheaper - it'll pay for itself before you know it.
Find a nice central point in the house that you can locate the switch and take a feed from there to each location you want Ethernet.
When I done my house, I pulled THREE cables to the lounge and dining room and office and one everywhere else. Remember, you can use the cat5/cat6 for more than just networking:
- Phone cabling if you need a wired handset
- Network
- Video signals (search for video baluns - you can send composite, HDMI (two cables, usually), audio), CCTV
- USB extenders (that use cat5)
I'm sure there is more too, but those are the main ones. Plan it out before you start or you'll kick yourself later.