Combinatorial Catalogues - - Combinatorial objects such as graphs, designs and geometries collected by Gordon Royle.
Combinatorial Data - - Brendan McKay's collection of miscellaneous tables in graph6 or sparse6 format.
The Combinatorial Object Server - - Select a type together with specific parameter values and COS will return a list of all such combinatorial objects.
Combinatorics - - Subfields in the AMS MSC 2000 classification 05.
Combinatorics - - MathWorld article with basic definitions and links.
A New Proof of the Four Colour Theorem - - By Ashay Dharwadker. Includes profile, research papers for other algorithms, lecture notes, and student database.