Azio E212U31 2.5" IDE to USB 2.0 Aluminum Enclosure for free after a $10 rebate and MClub membership. MClub is basically a free subscription to Mwave's discount and promotion emailing list.  Here is a screenshot for your reference.  Note that this is for converting a legacy 2.5" laptop hard drive into an external drive.  It does not need an external power supply and gets its power through the USB port directly for convenience.