One, like this one. Best I've had and still have. And I have tried whole bunch of them.
I wouldn't get any PCI wireless card anymore. Get instead USB, it has more power, faster reconnecting times and longer distance coverage.
I have Amped Wireless UA600 and after I got rid off my Linksys PCI card for this, What a difference that is. (I had this one and 2 others ... http://www.newegg.com/Product/Product.aspx?Item=N82E16833124342)
No more disconnections, PCI device slows down the boot time too. When I start the PC, type the password, and click on tom's HW shortcut, it is displayed in a second!
With that PCI (had 2 more to try) it started to connect after log in and it took few seconds.
Love it! My wife's iPad has about 6 networks to connect, I have about 40!
Linksys had about dozen.
Also this USB has 2 USB connections, for better strength, as it supply more power.http://www.newegg.com/Product/Product.aspx?Item=N82E16833281002