An old post, but just in case someone comes searching - Intel, 3Com, D-link, Atheros, and Linksys generally all have reasonable driver support. There are lots of wireless hardware compatibility lists around, if you care to search. For examplehttp://linux-wless.passys.nl/
For a more specific, current (April 2013) recommendation right here - I am using a TP-Link TL-WN851N PCI (not PCI-E) card in my Debian 6 PC with V2.6 Kernel.
It has an Atheros chipset and 'Just works' with encryption up to and including WPA2. As I write this, they are available on Amazon (and probably in other places as well). Several of the Amazon reviews specifically stated that it definitely worked under Linux - that's why I originally chose it.