Problems in Graph Theory and Combinatorics
- A collection maintained by Douglas B. West, of the University of Illinois. Features brief introductions, along with references cited. Topics include matching and independence, connectivity, graph homomorphism and circular coloring.
- http://www.math.uiuc.edu/~west/openp/

Open Problems in Combinatorics
- Features links to newsletters, workshops, and papers.
- http://www.combinatorics.net/problems/

Some Problems in Matroid Theory
- Thomas Zaslavsky of Binghamton State University of New York presents brief descriptions and references. Find information on Bonin's Projective Bound including the maximum r-flat, covering and packing by flats.
- http://www.math.binghamton.edu/zaslav/Matroids/matroidprobs.html

Past Open Problems
- From the SIAM Activity Group Newsletter in Discrete Mathematics. In PostScript. Compiled by Douglas B. West.
- http://www.math.uiuc.edu/~west/pcol/pcolink.html

Open Problems for Undergraduates
- A collection of open problems in Discrete Mathematics which are currently being researched by members of the DIMACS community.
- http://dimacs.rutgers.edu/~hochberg/undopen/