Princeton, a Japanese Manufacturer, has today announced the first (that I know of) physically write protectable CF memory, available as a Type I flash card in a variety of capacities (currently 32 to 256 MB) the card has a minute switch at the back which allows you to physically protect the contents from erasure / writing.

Click here for their press release (Japanese)

Although this is (as far as I know) the first CF storage card with the capability to be physically protected from erasure both SmartMedia and Memory Stick have had this feature since inception.