Differential Equations with Boundary Value Problems By S. Hollis (Prentice Hall, 2002). Overview of contents, errata, software and link to purchasing page. http://www.math.armstrong.edu/faculty/hollis/dewbvp
Introduction to Ordinary Differential Equations with Mathematica Contains a number of ODE labs, and an extremely useful Mathematica Package ode.m which allows series solutions of ODEs. http://math.cl.uh.edu/math/ode/ode.html
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. http://arxiv.org/abs/math.AP/9906155