You can start looking here: http://en.wikipedia.org/wiki/Comparison_of_open_source_wireless_drivers#Linux
It's probably not a perfect answer as it only lists chipset compatibility, but I hope it's at least a start.

I personally have a Netgear WN111, using it with hostapd as an access point. It is stable in G mode.
When I try to set it up in N mode, it seems to just stop responding under load.
I saw a couple messages on other lists that others have had the same problem. G is good enough for my use, so I stopped searching.

I have not tried it as a client.

Jeff

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]] On Behalf Of Joseph Areeda
Sent: Tuesday, March 26, 2013 2:22 PM
To: [log in to unmask]
Subject: Any recommendations for a compatible USB WiFi?

I tried to use the Broadcom WiFi that came with the motherboard (don't 
have the model number right now).

It seemed to not be recognized although Windows sees it fine in another 
system.

Would someone recommend a good USB Wifi that has current drivers for 
SL6.3?  Or point me to a list of drivers available in the release 
repositories?

It's a long story but we need both wired and wireless on this system and 
easier to buy a compatible interface rather than do much work to find 
non-standard drivers.

Thank you,

Joe