When your finished on this site, check out these....
Laci Babai's REU page An amazing resource! Links to handouts from 10 summer sessions. Great resource for puzzlers, teaching inspiration, and even some open problems.
Problems in Graph Theory and Combinatorics : Douglas West's excellent collection of open problems---includes details and status of each question.
Graph Coloring Problems -- The Archive: the online archives of the excellent book Graph Coloring Problems by Tommy R. Jensen and Bjarne Toft.