Other useful references are:

1. Generatingfunctiology - Herb Wilf (a free download)
2. Combinatorics: Topics, Techniques, Algorithms by Peter Cameron
3. Concrete mathematics : a foundation for computer science / Ronald L. Graham, Donald E. Knuth, Oren Patashnik.
4. Eunmerative Combinatorics Vols I, II, Stanley
5. Combinatorial Species and Tree-Like Structures (Encyclopedia of Mathematics and Its Applications, Vol 67) by F. Bergeron, P. Leroux, Gilbert Labelle (not in library)
6. Notes on introductory combinatorics / George Polya, Robert E. Tarjan, Donald R. Woods
7. Graphical Enumeration by Frank Harary, Edgar M. Palmer (not in library)