Differential Equations with Boundary Value Problems: By S. Hollis (Prentice Hall, 2002). Overview of contents, errata, software and link to purchasing page.
Green's Functions: Lecture notes introducing this technique for solving first and second order differential equations. Scanned (GIF) by Joceline Lega.
Pseudo-Differential Operators: These lecture notes cover a first year graduate course that was given on pseudo-differential operators. The calculus on manifolds is developed and applied to prove propagation of singularities and the Hodge decomposition theorem.
Series Solutions to Differential Equations: A set of downloadable lectures.
Vibrating Drumhead: A set of Mathematica packages which outline solutions of the wave equation in various coordinates.
Waves and Oscillations: Teaching resources developed by Frances Goldman, University of Glasgow.