Michele,
Every digital storage medium so far (and the hardware to read it) has become obsolete after a few years, and there isn't any prospect that will change anytime soon. So you can expect to have to migrate your files to newer technologies from time to time. There isn't currently any once-and-for-all solution.
For the current CD-R discs, use high-quality discs for your archives. There are some recommendations at
www.silverace.com/dottyspotty/issue12.html
Make at least two copies for your archives, stored in different locations. Do a 100% file verification check of each copy after it has been made. Store your archive files in raw, uncompressed TIFF format for lossless storage, rather than in compressed formats such as JPEG, and especially not in a proprietary format that may not be supported in the future. Protect your discs from sunlight and heat, which can destroy your discs quickly. Keep your archive discs in individual hard-shelled jewel cases to protect them from mechanical damage. Do not put adhesive labels on your archive discs, as the adhesive will deteriorate over time. Migrate your files to the next generation technology in a timely fashion.