OR-Library is a collection of test data sets for a variety of OR problems.
A full list of the test data sets available in OR-Library can be found here.
There are currently 15 data files. These data files are the test problems solved in J.E.Beasley "A heuristic for Euclidean and rectilinear Steiner problems", European Journal of Operational Research 58 (1992) 284-292. Information about these test problems can be obtained here