1. Harary's book is great - and he's a hoot. 2) Ringel and Hartsfield's Pearl in Graph Theory is great, lovable and has lots of pictures and excellent exercises - ideal for an undergrad class that's not geared towards prepping students towards a grad course. 3) Gross and Yellen's book is probably the best introduction if you're a "mature" math reader and want to really learn stuff - this is what I would buy. 4) Applied Combinatorics by Tucker is phenomenal - but graph theory is only 4 chapters out of 11. Nonetheless, I'd strongly consider this one.