A couple of years ago I added HomePlug AV powerline-networking support to my Wi-Fi network, and I've never looked back. It's particularly useful in my home entertainment center, where I have four networked devices connected via ethernet to a four-port HomePlug AV switch plugged into a wall outlet.
I enabled the powerline network by plugging a HomePlug AV adapter into a free ethernet port on my Wi-Fi router at one end, and into a wall outlet on the other. But a couple of vendors are starting to ship hybrid routers that support both Wi-Fi and HomePlug AV, out of the box. The D-Link DHP-1320, for one, announced at CES, is shipping for as little as $100 (but it doesn't support 5GHz 802.11n, only the 2.4GHz flavor).
HomePlug AV powerline isn't as good as gigabit ethernet, but in general it has proved more reliable than even 5GHz Wi-Fi for streaming media. Unless the electrical circuitry in your home is really old, it can be a great substitute--and of course, it doesn't require running new cables behind walls.
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