Just to say thank you to everyone who responded - it was very helpful and I took the advice about using my Ipod to back up the images. I hadn't realised this was possible but I bought a £19 Ipod Camera Connector and have successfully backed up a test batch. Perfect!

Sorry I should have been more specific - I'm going to Japan on holiday and anticipate taking a lot of photos each day with my new Pentax k100D. I have a couple of 2GB SD memory cards but I'm nervous that they may fail at some point towards the end of the trip and I might lose all my images. So I was considering backing them up onto a Portable Storage Device at the end of each day just in case.

Can anyone recommend a reasonably priced Digital Photo Storage Device that will take SD memory card?