Netgear G54/N150$25.00 recommended
The Netgear dongle is high quality and very compact. Ideal for Raspberry Pi projects. Connection quality is great. This usb adapter supports wireless-n, b and g.
AirLink101 AWLL5088$13.00 recommended
The AirLink101 adapter is probably the smallest wireless-n capable USB adapter you will find. It's small size is ideal for Raspberry Pi projects.
The dongle itself is cast in a slightly cheap-ish white plastic housing with a built-in green LED status light and WPS button.
Well, in a nutshell you get what you pay for. This thing works. And that's about the only good thing I can say about it.