Cowboom offers the used 2nd-generation Apple AirPort Express 802.11n Wireless Base Station, model no. MC414LL/A, for $44.99 plus $5.24 for shipping. That's $10 under our refurb mention from November and the lowest total price we've seen for this model. (It's also $39 under the best price we could find for a new unit.) This device uses 802.11n to play iTunes over your wireless network to your home stereo, acts as a wireless router, and enables wireless USB printer sharing.
Of note, no warranty information is provided.