wireless network adapter

I want to set up a wireless network. I have a netgear router on the first floor and on the second floor (thru one wall and ceiling) is my computer. I was using a Dlink 650 wireless card but couldn’t get a reasonable signal to get on the internet.I’m thinking about getting a USB wireless adapter but was wondering which adapter has a good signal strength. I’ve tried looking through the web but haven’t found anything comparing USB wireless network adapters.