You have 2 x PCIe x1 slots on your board. If one of them is not blocked by a gfx card, and you want to use a wifi card instead, here are the best rated ones according to users at Newegg: http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100010074%20600014297%20600014354%204814&IsNodeId=1
I haven't personally used any, so I can't vouch for them. However D-link, T-P Link, Intel are good brands.