GEOS 530 Environmental Systems Modeling I
Very good discussion of the Navier-Stokes Equations.
GNU Operating System; Much great software from the Free Software Foundation.
GNU Package Blurbs; Short descriptions about the many available packages.
Units; A GNU program for many useful unit conversions.
Netlib Repository; A massive collection of math software, papers, and databases.
Water Applications: USGS Water Resources Applications Software.
EPA Databases and Software: Air, Pollution Prevention, and Water.
NCAR Earth Observing Lab: Data Analysis and Equipment Software. Huge collection!