Do have a look at the
HP SimpleSave Portable
This is a USB connected portable separate hard drive. It has integral software, which makes both Backup and Restore a breeze. It sits there in the background, quietly handling Backup and you don't have to do anything other than set it up to start with and then just wisely check on it every so often to see if it is continuing to do its stuff.
It comes in various sizes from, say 320GB (circa 55-60) right up to 2TB (circa 150)
I like it and use one myself. I think it is a great value combination of portable hard disk and automated backup software.
There are some videos on it
here.
You can use the Google Shopping (a tab off Google) to see where to get it from in the UK. I bought mine in Tesco.
You could also look at Acronis' True Image Home 2010, and another type of separate USB disk, such as Iomega's eGo Portable.