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, 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, 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, Ax = b, using the Unsymmetric MultiFrontal method. http://www.cise.ufl.edu/research/sparse/umfpack/