String theory notes on the web

These ones give a broad overview:

David Tong: Lectures on String Theory given to Part III students at Cambridge.
Eric D'Hoker's lectures on String Theory given in Spring 1997 at Princeton and printed in the book Quantum Fields and Strings: a Cource for Mathematicians can be found here in the .dvi or .ps format, or the .tex source.
Lectures on String Theory by Liam McAllister at Cornell; LaTeXed notes by Flip Tanedo.

These ones are more focused on various topics within string theory:

String Calculus: Conformal Field Theory as a Tool in String Theory (KEK scans) by Emil Martinec. Lectures from the 1987 Trieste Spring School.
String Theory on Calabi-Yau Manifolds by Brian Greene, these lectures closely follow a series of seven lectures given at the TASI-96 summer school on Strings, Fields and Duality.
Differential geometry in string models by Orlando Alvarez: KEK scans. Lectures from the Workshop on Unified String Theories, Santa Barbara 1985.
Les Houches Lectures on Fields, Strings and Duality by Robbert Dijkgraaf, given at the 1995 Les Houches school.
Riemann Surfaces And String Theories by Luis Alvarez-Gaumé and Philip Nelson (1987).
Lectures on D-branes by Constantin P. Bachas (1998).