What freely available graph theory resources are there on the web? In particular, I am interested in books and lecture notes containing topics such as trees, connectivity, planar graphs, the probabilistic method ect., though no resources is expected to be comprehensive.
Note that I have searched MathOnline, which yielded the book Graph Theory by Reinhard Diestel. This resources seems to be good, but I prefer to have multiple resources when studying a topic.
Note: I am aware of the many questions on this site regarding book suggestions for particular topics. While this question is related, I am only interested in freely available resources, as I am a broke college student.