Tables

ATLAS of Finite Group Representations - Representations of many finite simple groups and related groups such as covering groups and automorphism groups of simple groups. Available by FTP in alternative formats: Meataxe ASCII, Meataxe binary, and GAP.
web.mat.bham.ac.uk/atlas/

Collapsed Adjacency Matrices, Character Tables and Ramanujan Graphs - A database of character tables of endomorphism rings.
www.math.rwth-aachen.de/~Ines.Hoehler/

Groups of Small Order - A list of isomorphism classes and further information on groups of order up to 30, by John Pedersen, University of South Florida.
www.math.usf.edu/~eclark/algctlg/small_groups.html

Small Even Order Groups - Generators for small even ordered groups from 1 to 1000. Files use gzipped extensions and require downloading.
www.csse.uwa.edu.au/~gordon/remote/cubcay/

Test Polynomials for Galois Groups - A table of polynomials for Galois groups over the rational numbers with degree up to 9. The table includes links to additional information for each equation.
world.std.com/~jmccarro/math/GaloisGroups/GaloisGroupPolynomials.html