Are you sure you'd like a wifi card?  A USB adapter would be cheaper.  MSY has a  TP-Link TL-WN725N 150Mbps Wireless N Nano USB Adapter for $9 that the Amazon reviews say is quite sensitive.  MSY also has a TP-LINK TL-851ND PCI 2T2R Wireless-N 300 Network Adapter PCI card for $19.