Enthused by the success reported in this blog post, I purchased a couple of Wi-Fi wireless N USB dongles from this ebay seller for use with my Raspberry Pi:

The chipset in this dongle is the Ralink RT5370:

The build quality was pretty good for something that cost a fraction over $5 delivered!

This dongle worked out of the box with Raspian Wheezy 2012-08-16. It seems to work fine powered directly from a Raspberry Pi USB port (i.e. without requiring a powered USB hub to be interposed). However, when I plugged it in, it caused the Raspi to reset. After the reboot, the wireless interface came up fine. So it may be safest to connect the dongle with the Raspi powered down. Alternatively, use a powered hub.

After inserting the dongle, here’s what I got as output from lsusb and lsmod:

I then added this stanza to /etc/network/interfaces, substituting the actual network SSID and WPA password:

Finally, I enabled the interface and verified that all was working as expected:

(Note I observed link bit rates between 1Mb and 54Mb when associated with an 80211g router.)