A similar question was asked [here][1]. At the time I suggested Donald Knuth's Stanford GraphBase: A Platform for Combinatorial Computing (1994, 2009) and the accompanying [website][2].

See also [The Stony Brook Algorithm Repository][3].


  [1]: https://mathoverflow.net/questions/23748/where-on-the-internet-i-can-find-database-of-graphs/23761#23761
  [2]: http://www-cs-faculty.stanford.edu/~uno/sgb.html
  [3]: http://www3.cs.stonybrook.edu/~algorith/implement/graphbase/implement.shtml