If you want to read in depth about CD-R hardware, software, and media, one outstanding resource is Andy McFadden's CD-Recordable FAQ. The FAQ is huge--it's been around for five years, dating back to the time when CD-Rs first became affordable--and it's still updated about once a month.
I've found that the quality of CD-R products has improved to the point where simple empirical experimentation works fine. When you get a new CD-R burner, buy a variety of CD-R blanks in small quantities, and try them all. Once you know what works (and chances are, with today's CD-R drives and software, almost everything will), buy in bulk quantities for the best prices. Currently, the best standard, nonsale prices I know of are about 18 cents per blank 650MB/16x CD, in bulk. At 18 cents a pop for a backup medium that will last more than 10 years, it's hard to go far wrong.
What's your take? What have you found that works well for short, medium, and long-term backup? If you're using tape, what steps are you taking to ensure long shelf life? If you're using CD-Rs, what types do you prefer, and why? What sources do you use for buying blank media? How long do you think your data will survive in storage? Do you periodically refresh old backups by re-recording onto new media? Please join in the discussion and share your knowledge!