The one I used to in my previous project to some extent was
BerkeleyDB, but again - I still haven't looked properly at the work of igorsk & others so I don't know the platform limitations and BerkeleyDB might be a little overkill here.
SQLite is another option which is quite widely used in embedded systems (think iPod/iPhone), but I don't have any personal experience with that.
Anyway, thanks for the reply and consideration of the suggestion!