Given unlimited money, I would just buy a notebook with a CD-R drive. This would give me multiple gigabytes of portable hard drive, the security of a second copy of the data before I erase the memory card, and a way to display images to people without having to make prints. But money is limited.
I will probably buy a second 1GB card, for the same reason that I have a second battery for the camera -- I want to be able to a quick swap and keep going. But after the second 1GB card, I think the right direction is some sort of battery powered device with a hard drive in it. The problem is that the inexpensive ones that I'm aware of allow you to copy image files off of a CF card, but don't provide any ability to view the pictures to verify that the copy worked. Units that can display pictures as well as store them seem to approach the cost of a notebook.
If anyone reading my journal has sage advice, please offer it.