If you're going to store anything with archival value, meaning you want it to still be there two or three years time, then burn to a DVD. Computer CD's can and do fail. If you really want to be certain, make a second back-up on an external hard drive.
Stu -
a memory stick or other device is ok, but their primary intended use is not so much long term storage, but for transferring files from one computer to another. Some memory stick devices may fail due to shock (ie, dropping it), proximity to magnets, etc. They really should be considered only temporary storage.
With a laptop, if it's USB compatible I'd go with an external DVD burner (SONY makes a very reliable model). You could also use an external Hard Drive, but these can be bothersome -- usually they're good for storage, not as good for accessing files and using files from the hard drive. Meaning, if there's a file on the external you want to use - modify, edit, etc -- it's usually better to copy it onto your computer's hard drive and store it only on the external.
The number biggest drawback of a laptop - limited storage space. With a desktop computer, you can add or expand existing hard drives relatively easily. And the prices keep going down on hard drives as the volume of storage is going up! I've got a 70 gb and a 30 gb, and I'm thinking of dumping the 30 to get 100 gb!
crazy!