Cluster Lenses Kneib and Nataranjan
Weak lensing- Schneider
Astronomy/Astrophysics on the Internet- A collection of resources
Prof. N. Kaiser's Lectures-Elements of Astrophysics
Essential Radio Astronomy- Nice description of physical processes
Notes on X-ray Optics; Dan Schwartz
X-ray telescopes- Encyclopeda of Astronomy and Astrophysics
X-ray schools web pages and other useful material