Some of those wireless add-ons are designed to support external antennas. They don't advertise it, but if you have reception problems and aren't afraid of taking things apart, there's a pretty good chance that the circuit board will have the traces needed to allow you to solder on an SMA connector for an antenna...the engineers know that the internal antennas are crap and keep hoping that the marketing department will let them make something that works right.

More ideas:
http://www.turnpoint.net/wireless/has.html