Get used to hearing the word 'dongle' in casual conversation, because Apple is shipping one for the MacBook Air
-- an Ethernet to USB adapter
for those who absolutely must use a wired network. For $29 you get a 10/100Base-T Ethernet connection and the opportunity to use up your one USB port for connectivity (hint: either get used to typing on the full-size keyboard on the laptop, or pick up a small USB hub). It's not the fastest gun in the West but it will certainly get the job done.