You can make your own long-distance WiFi accessory from various items, but Hawking Technologies has another option if hacking isn’t your thing. The Hi-Gain Wireless-300N is a high-gain dish adaptor that will hook up via USB and can apparently extend wireless range by up to 600-percent. Supporting WiFi in b, g and n, they also claim to give you up to twelve times the data.
They are calling it “the most powerful 802.11n USB network adapter on the market”, and it supports WEP, WPA and WPA2 encryption. Another selling point is the dual-antenna. The idea is that you can avoid signal interference by pointing it away from other electronics, though I’m not sure that’s a big problem for most people.