WiFi is great until you start reaching the fringes of your router's range, at which point throughput slows to a trickle and you start dreaming of nice, reliable ethernet cables. Happily there's an alternative to snaking CAT-5 around your skirting boards; Open-Mesh makes Mini-Routers that, when plugged in and registered, automatically create a mesh-network and thus boost your WiFi coverage.
Mesh networking is one of the more interesting elements of the OLPC XO-1 notebook. Since it's intended to be used in areas where standard network infrastructure is patchy at best, the XO-1 can form an ad-hoc mesh by linking with other XO-1's. That way internet data is passed between notebooks and spread out from the original connection, without needing to install cables or even WiFi repeaters.
Of course, even if your plans are slightly less ambitious (or less altruistic) than that of the OLPC project, the Open-Mesh Mini-Router could still come in handy: extending WiFi coverage down to an outhouse or guesthouse, perhaps, or quickly boosting connectivity in a bedroom far from the router. Two networks can run concurrently, one open (for guests) and the other WPA secured (for your own use). There's a variety of bandwidth throttling and firewall options, and by plugging a non-wireless device into the ethernet port that can get online too.
The Mini-Router is available now, priced at $49 for one; or, if you want 20 of them, $799 (which works out to $39.95 each). Alternatively, since it's all based on an open-source project called ROBIN, you can flash a compatible router yourself should you be feeling technical.