Harmonic Function Theory and Mathematica
Performs symbolic manipulation of expressions that arise in the study of harmonic functions. This software is available electronically without charge.
L.L.Helms Homepage
Author of 'Introduction to Potential Theory'. Contains information about his forthcoming book 'Potential Theory, the Dirichlet Problem, and the Other Problem'.
Northern Illinois University - Mathematical Atlas
Gives a brief description of potential theory with some indications of textbooks/tutorials and links to other web resources.
Potential Theory
Karlin's page, which is a good place to find out who is doing work in potential theory.