It’s been mentioned in our forums but In case you haven’t been through their parts drawers of late, Radio Shack has started carrying Parallax sensors in their retail shops. You’ll pay a bit of a premium (~$3-$10 more) for picking them up there as opposed to ordering from somewhere else – but it’s good to know the brick-and-mortar option’s available. –Link

Parallax RFID Reader – MAKE:06 p.162 –Link