ARPACK is a collection of Fortran77 subroutines designed to solve large-scale eigenvalue problems. http://www.caam.rice.edu/software/ARPACK
The ATLAS (Automatically Tuned Linear Algebra Software) project provides C and Fortran77 interfaces to a portable efficient BLAS implementation, as well as a few routines from LAPACK. http://math-atlas.sourceforge.net
The Harwell-Boeing matrix format is a popular storage and description format for sparse matrix data, described at http://math.nist.gov/MatrixMarket/formats.html. Many examples of matrices in this format can be found at http://math.nist.gov/MatrixMarket/index.html.
The Matrix Market matrix format provides a simple mechanism to facilitate the exchange of sparse and dense matrix data, described at http://math.nist.gov/MatrixMarket/formats.html. Many examples of matrices in this format can be found at http://math.nist.gov/MatrixMarket/index.html.
METIS is a family of programs for partitioning unstructured graphs and hypergraphs and computing fill-reducing orderings of sparse matrices. http://www-users.cs.umn.edu/~karypis/metis/index.html
TAUCS is a library of sparse linear solvers. http://www.tau.ac.il/~stoledo/taucs
UMFPACK is a set of routines for solving unsymmetric sparse linear systems, , using the Unsymmetric MultiFrontal method. http://www.cise.ufl.edu/research/sparse/umfpack
 Weisstein, E. W. MathWorld 2007. http://mathworld.wolfram.com
 Anderson, E., Z. Bai, C. Bischof, S. Blackford, J. Demmel, J. Dongarra, J. Du Croz, A. Greenbaum, S. Hammarling, A. McKenney, and D. Sorensen. LAPACK Users' Guide, 3rd ed. Society for Industrial and Applied Mathematics, 1999.