I have used MacAlly multi-Interface 3.5" external cases from Amazon, and have been happy with them. I bought the ones with Firewire 800, and that can provide a fairly speedy backup.
For re-purposing laptop drives, I have used the OWC Mercury Elite Pro metal mini-enclosures.
2.5" drives are mostly laptop drives, and use a 5 Volt spindle motor. They are not performance drives. You CAN Bus-power them, but a power supply of some description (even a USB stunt cable) may be more reliable.
3.5" drives are desktop drives, and use a 12 Volt spindle motor. Their enclosures MUST have a power supply of its own. They have the potential to be faster.