One of my buddies had a Thermaltake Mobilefan that he had but wasn't using anymore that he gave me. It is an 80mm external case fan that runs off a USB cord. So I'll be able to plug it into the wall and hook it up to an old Ipod charger.
Regardless of brand - you're probably going to want to put it on an adjustable power supply so there isn't a small hurricane inside your tank. I had a teeny 40mm fan that vibrated in its PVC housing very loudly on 12v - it also was drying things out a little too quickly for my liking.
They have them at Walmart for like $10 in the electronics section. I re-watched Jame's video before I hooked mine up. My hands shake a lot sometimes so I wished I had gotten the helping hands alligator clip thingy he had in the video.