I am a little bit into wifi. have builded few antennas myself . I have a dish reflector antenna which exceeds 10miles. Using Senao 200mW PCMCIA adapter.
I have a USB wifi (belkin) and waiting for connectors to modify it by adding external antena socket (SMA). Hombrew antenna i will build, is on this site: http://martybugs.net/wireless/collinear.cgi
Many people saing that orinoco cards are good.