One of the handiest accessories you can have is extra memory. A couple of extra memory cards can assure that you won't be stuck at a critical moment. Imagine needing - and not having - a spare memory card during your daughter's first dance recital, or at your sister's wedding.
Additional memory is affordable and necessary, and if you shoot a lot pictures, don't bother with anything less than 256 MB. Smaller cards will feel like 12-exposure rolls of film: used up before you barely get started.
And don't forget to take your camera's resolution into consideration. An 8 MP camera will chew through memory fast.