Depends on how much time, money, and effort you want to put into it.
For a real computer guy or someone who's building a new house, I'd recommend running gigabit ethernet everywhere you could ever possibly want a computer (don't forget the kitchen, den, or anywhere else you could conceivably drag a laptop.) If you're comfortable running lots of wire, regular old 10/100 will be just as good for usual uses.
Really though, that's just the computer guy in me talking. For simplicity and low cost of installation, you really can't beat wireless. I have a D-Link based system in my house and I put together a Belkin based system in my ex's parents' house. I think I spent $50 on her router and maybe another $50 on a wireless card for the second computer (her laptop had one built in.)
I've never had a problem reported to me about the system in her parents' house, except for the one time her younger brother buried the router under a pile of dirty clothes and wondered for weeks why the second computer had no signal (not the cleanest kid around.)
Here in my house, I've had problems with Windows XP trying to take over control of the wireless card on the second computer a couple times (maybe four times in the two years it's been up.)
My advice is get whatever letter (802.11a/b/g) fits your price range and distance requirements (g and b have much better penetration than a does). *Follow the instructions in the manual to the letter* when installing the card and configuring the router. For both of the brands I've worked with, some of the directions they give you are not in the natural order I would do things; but, I followed the instructions and had zero problems with installation. I've seen a lot of message board posts from people who did things backwards and had some trouble correcting their mistakes later. This may be one time when less computer experience is actually more helpful
And don't worry about speeds. All three standards are faster than your cable modem is. 802.11g is only worth it if it's about the same price as a 802.11b solution, or if you do a lot of between computer transferring.