The Most Long Lastingest Storage?

What digital storage can retain information the longest? Recordable CD/DVDs only last a couple of years. A decade at most. Barring catastrophic disk failures, HDs seem to last the longest, but what about Flash Memory? These types of memories are increasing in capacity rapidly and they don't have any moving parts.

In 100 years, who's gonna care what's on the stick?  Archaeologists, maybe, but not a whole lot of others.  And those who do, will probably have all the legacy systems they need.