People go to great lengths to avoid running wires, and for the most part, in my opinion, it's foolish. You'll spend the same order of magnitude $$ to run cat5 cables and use wired Ethernet as you'd spend to do powerline networking, phoneline networking, or wireless (okay, wireless is getting dirt cheap fast, so the cost really is cheaper now). And for that, you get a slower, less reliable solution that probably doesn't have a future.
You're best off running the cables. They'll carry you quite reliably up to 1000BaseT, which should keep you happy for many years. The alternatives should basically only be used when running cables really truly isn't an option (and sometimes, it just isn't). Among the alternatives, I agree with the previous posters - go wireless. The simple reason is scale - it's easily available, cheap, multi-vendor, and mostly debugged now. That's not to say it's necessarily a technically better solution, but that following the market has some advantages that outweigh a lot of the technical factors.