Potential Theory

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.
http://www.axler.net/HFT_Math.html

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'.
http://www.math.uiuc.edu/~l-helms/

Northern Illinois University - Mathematical Atlas
Gives a brief description of potential theory with some indications of textbooks/tutorials and links to other web resources.
http://www.math.niu.edu/~rusin/known-math/index/31-XX.html