Online handbooks for mathematical tables and formulas.

CRC Standard Mathematical Tables and Formulae

Handbook of commonly used equations, tables, and formulae.

Encyclopaedia of Mathematical Sciences

Major mathematical specialties are covered by a sequence of volumes (e.g. Topology, Geometry, Algebraic Geometry, Several Complex Variables, Analysis, Lie Groups and Lie Algebras, Number Theory, Partial Differential Equations, and Dynamical Systems).

Encyclopedia of Mathematics and its Applications

This series is devoted to comprehensive coverage of significant topics that have wide application in mathematics and for which a detailed development of the abstract theory is less important than a thorough and concrete exploration of the implications and applications.

Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables

A compendium of mathematical formulas, tables, and graphs. It contains a very complete table of analytical integrals, differential equations, and numerical series; and includes tables of trigonometric and hyperbolic functions, tables for numerical integration, rules for differentiation and integration, and techniques for point interpolation and function approximation. Additionally, the book devotes an entire section to mathematical and physical constants as fractions and powers of Pi, e, and prime numbers; and discusses statistics by presenting combinatorial analysis and probability functions.

Handbook of Mathematics (6th Edition)

Contains in handbook form the fundamental working knowledge of mathematics which is needed as an everyday guide for students and scientists.

Mathematical Methods for Scientists and Engineers

Comprised of more than 2000 problems and 700 worked examples, this text is useful for self study.

Wolfram Functions Site

From the producers of the Mathematica software, this site is a compendium of information for mathematical functions.