Andries Brouwer's collection of strongly regular graphs: http://www.win.tue.nl/~aeb/graphs/srg/srgtab.html

Eric Moorhouse's collections of finite projective planes and generalized polygons: http://ericmoorhouse.org/pub/planes/, http://ericmoorhouse.org/pub/genpoly/

Gordon Royle's collection of combinatorial objects: http://staffhome.ecm.uwa.edu.au/~00013890/data.html