My research is in combinatorics, and includes the study of such structures as difference sets, strongly regular graphs, and association schemes. I also study integer-labeled graphs, in particular magic graphs and perfect distance graphs.
A difference set is a special subset of a finite group, and corresponds to a symmetric design with a regular automorphism group. There are some good online resources for these sets, for example:
A Survey by Dr. Ken Smith (Sam Houston State University)
La Jolla Difference Set Repository
Partial difference sets are my personal favorite object of study, and they correspond to strongly regular graphs (SRGs) and projective two weight-codes. There are useful tables online for these structures:
Brouwer's Homepage (Includes a table on SRGs)
Online Database of Two Weight Codes