If its just key pair stores, apparently nosql style databases work well - twitter does use these, and they might be a great fit if you need to handle a lot of data with very little structure. You could probably use a traditional rdbms, or maybe an embedded sqlite db if there are more than a simple key pair store and had structured data with relations.
It might also help to understand the weakness of a flat file store (no transaction logging or structure), nosql (no ACID) and a traditional db(bulky, less scalable but well understood and often reasonably fast). With a small non updated set of data, any of them should work