Here's a nifty little 2.5" HDD external enclosure. Put your own drive in, then throw some .ISO files on there and you can then select the ISO file from the onboard LCD screen and buttons. Then plug the device into a PC via USB and the PC will see it as a CD-Drive with that ISO up and running. (Basically it pretends to be a CD-ROM drive)
This is perfect if you re-install PC's, or can't be bothered to burn CD's or USB keys for Linux distributions or other similar activiities. The drive also acts as a standard USB External HDD also.
Seems pretty smart .. may be more pricey than a usual enclosure but way more useful if you do this sort of thing often and will pay for itself in saved time alone!