www.mpi-forum.org: The official MPI Forum Web site, contains Postscript and HTML versions of the MPI-1 and MPI-2 Standards.
www.mcs.anl.gov/mpi: A starting point for information about MPI, including libraries and tools that use MPI and papers about the implementation or use of MPI.
www.mcs.anl.gov/mpich: Home of the MPICH and MPICH2 implementations of MPI. Download source, documentation, and Unix and Windows versions of MPI from here. Also check the bug list page for patches and announcements of releases.
www.netlib.org: A valuable collection of mathematical software and related information.
www.csm.ornl.gov/pvm: PVM home page.
www.mcs.anl.gov/romio: Home of the ROMIO implementation of the I/O chapter from MPI-2. ROMIO is included in MPICH and LAM but can also be downloaded separately. Information on tuning ROMIO for performance can be found here.
hdf.ncsa.uiuc.edu: Home of HDF. Included here are I/O libraries; tools for analyzing, visualizing, and converting scientific data; and software downloads, documentation, and support information.
www.parl.clemson.edu/pvfs: Home of PVFS, a parallel file system designed for Beowulf. This site includes online documentation, FAQ, source code downloads, mailing lists, developer's area, and research papers about PVFS.
www.cs.dartmouth.edu/pario: Home of the Parallel I/O Archive. This includes a list of projects in parallel I/O, people working in parallel I/O, and conferences on parallel I/O. Its biggest claim to fame is an extensive annotated bibliography of parallel I/O resources.