One of the best, or simply the best WiFi card ever made to the public, is the Orinoco Wireless PC Card.
It has an outstanding performance, and I have used it from various tasks, ranging from Warwalking, wardriving with laptops, pocket pc with pcmcia expansion kits, to working as the sole network adapter on a wireless server of mine. Besides that, it works great with a bunch of software, like Kismet, Netstumbler, Ministumbler, Airsnort, Aircrack etc.
The Orinco card has a security level that provides 802.1x authentication and encryption up to 152-bit WEP. It includes a built-in connector for an external Range Extender Antenna for longer distance connection. I have been using the Orinoco cards since late 2001, and am one really satisfied Orinoco user.
So if you are looking for a wireless card that really works, go Orinoco. Unix/Linux, Microsoft Windows and Mac OS, Pocket PC, Windows Mobile.