The Astone ISO Gear 481E 3.5" external disk enclosure connects through eSATA and USB 2.0. There are no noisy cooling fans and the price is reasonable. Update June 2011. See Astone ISO gear 481U3 external enclosure for 3.5" disk with a USB 3.0 connection for the USB 3 version.
At the time of writing, shops have the 481E at AU$30 up to AU$90 then they have packages of the 481E plus a disk at prices going up over AU$300. Put your own package together to get the right brand and size disk at the right price.
Disks make noise. Hitachi and Samsung have disks and both are reasonably priced. The Astone 481E does not add noise because it does not need a cooling fan. The side panels of the case are open mesh to let cooling air flow through without wasting energy on a fan and without the whining squeal of a fan. The combination will be quiet if the disk is quiet.
Given that the only noise from this device is the disk, your choice of disk is critical. There is a big variation between disk brands and most brands now have several ranges of disks with different noise levels. Some models are quiet when spinning then make annoying clicking noises when the read/write heads move. Some models are noisy all the time. There are also models with the option to set the disk to produce less noise or use less power. The low power and low noise options almost always produce a slower response time.
Samsung have regular disks running at 7200 rpm and low power versions working at the slower 5900 rpm. Both ranges are reasonably quiet compared to equivalents from other brands. Unfortunately Samsung, like many other brands, often have several models in each price/performance range and, if you get the wrong model, the noise and performance will be different from what you expect after reading reviews. A recommendation or review of a disk applies only to the exact model tested.
What you want is a disk that you cannot hear when it is idle and is not distracting when operating. Some new disks will power themselves down when not in use, reducing the idle noise. Those disks may be distractingly noisy when they power back up.
Assembly is as easy as you can get for a metal box containing a disk. A small phillips head screwdriver is the only tool needed. You remove both metal mesh side covers. You slide the disk in one side and lock the disk in using screws from the other side. You then replace the metal mesh covers. Watch the edges of the metal mesh when placing the sides back in the frame. The following image shows the case with one side panel removed and an old disk inserted for a test.
The packet says 1.5 TB (TeraBytes) and the manufacturer says 2 TB. My 2 TB Hitachi disk is working happily in the 481E.
USB 2.0 is the current practical standard for USB. USB 3.0 components are arriving daily but cost twice as much and you cannot use them with existing computers. You can buy USB 3.0 add-on cards and things for existing computers then you find they work only with some versions of operating systems, you find the maximum cable length is only three metres instead of 5 metres, and a few other problems.
USB 2.0 is great with existing computers. USB 2.0 is ok for backups and a very good choice for a backup that is moved between a notebook and a desktop. USB 2.0 is faster than you need to store large collections of music, software, and videos.
USB 3.0 will be practical when you have replaced all your existing computers with new computers. USB 3.0 could then replace eSATA.
eSATA is the best connection for large scale backups and is, in practice, as fast as USB 3.0 because both are faster than your disk plus eSATA has lower overheads. The one disadvantage of eSATA is the very short cable. To use eSATA, you have to put the disk next to the computer. Usually the eSATA connection is at the back, making the connection even more difficult. USB 3.0 will let you connect more easily because you can have longer cables and, one day, new desktop computers will have a connection at the front of the case.
Update June 2011. Buy USB 3.0 for all modern disks. See Astone ISO gear 481U3 external enclosure for 3.5" disk with a USB 3.0 connection for the USB 3 version. The Astone 481U3 is the best of the USB 3.0 external enclosures because of the reasonable price and no noise.