Ok, the first thing I learned when building my wireless network was cheap was never the right choice... go for quality. Next you need to decide what you really want, strong signal strengths or a lengthy battery.
Once you have decided that head over to Seattle Wireless at this link:
http://www.seattlewireless.net/index.cgi/Client_5fAdapters_5f802_5f11b
its a great list of wireless client cards and their specs, however you will have to do the research to see if drivers for your OS are available. I can tell you I have the Senao 2511 that has the external antenna ports and a cheap 3" whip that plugs directly in and I get great signal strength.. however it doesn't exactly prolong my HPC battery, but who needs battery life when I can connect 1/4 mile from a good AP?
