Regular reader Wolfgang sent me an encryption concept a few months ago. At first glance, it looked like a really good idea. Unfortunately I haven’t had the time to delve into it, but you can. See Encryptor-Decryptor.
It encrypts only locked cells in select worksheets, so that you can “partially encrypt” a workbook, leaving some cells accessible and visible, and others inaccessible.
Somebody download it for the 5 free days and tell me what you think. I didn’t note a price on the website, which would probably influence my decision. Also, I encourage the developers to make the trial 30 days; five just isn’t enough.