Pressed optical media (Score 1)

I don't know what your cost constraints are, but if you want optical media that won't degrade over time, go to a duplicator and get your data pressed onto the ubiquitous optical media of your time. A professionally pressed DVD will not degrade like a burned DVD because it actually makes pits in the media, as opposed to just manipulating a dye.

Repeat this process every decade or two and you should be in okay shape. This is of course assuming that optical media continues to be relevant. If we end up back at magnetic (or FSM forbid cloud) storage, it gets trickier.

FWIW, it'd be interesting to know more about this data. Any particular reason it can't be printed out into a book or onto microfiche? The only long-term important media to me is stuff that lives on after I do, and that's really means diaries/logs and photos.