I have a 20 GB Smartdisk which has worked just fine at backing up my photos and it comes without a screen viewer. I like it because it is so small and compact and the battery life is very good.
In terms of your questions, it really depends what you want. If you do want to view your pictures, then get one with a viewer but realize that this will cost you. You should also consider things such as battery life, speed and compatibility with your computer. Most of these devices should just show up as another drive on your computer without the need to install a program.
Check out this
Buyers Review.
The Nexto also looks pretty good and may fit your requirements. I think you can purchase this and others in Australia via
Buy.
Just be aware that these storage devices are just the same as regular hard drives and are subject to failure. So I would also consider an alternative backup system as well such as an online storage site like Flickr. Check out this earlier thread on the subject (
Backing up).