External Enclosure

I'm looking to purchase an external enclosure for a spare HD I have lying around. I was looking for any suggestions you guys could provide. It'd only be used for a HD so 3.5" is all thats necessary (although if a 5" is cheaper, I could go for that). No firewire here so that's unimportant. My main concerns (besides functionality obviously) are heat and price. I'm not sure if a built-in fan is necessary. Also, I'd like to go small if possible but that's not a great concern. Thanks.