There's the "STL Programmers Guide" ( David Musser, Atul Saini Addison-Wesley, 1996, 400 pages, stl_tutor_ref, ISBN 0201633981) It's not free, but IMHO definatly worth the money. It explains STL, the ideas behind it and the way to use it better than any appendix in any general C++ book I've seen so far.