Depending on what you can spend and routers capabilities,the next options,
http://pcpartpicker.com/parts/compare/asus-wireless-network-card-pceac68,gigabyte-wireless-network-card-gcwb867di,tp-link-wireless-network-card-tlwn822n/
i have both the cheapest and most expensive,both work well,the cheapest is limited to the 2.4ghz band and limted in performance by that.The Gigabyte has still both bands to use,2.4/5ghz,and has bluetooth as a bonus.These have a movable antenna which i favor for the best signal.
There's a dualband version of the cheapest one,though more expensive of course...