Why Wormholes? - Brief article by Matt Visser (Victoria University of Wellington) about why the concept of a wormhole, originally more science fiction than science, has become interesting for serious physicists. - http://www.mcs.vuw.ac.nz/~visser/general.shtml#why-wormholes
What Exactly Is a 'Wormhole'? - From Scientific American's "Ask the experts", with answers by Richard F. Holman, William A. Hiscock, and Matt Visser. - http://www.sciam.com/askexpert_question.cfm?articleID=000998FD-65C6-1C71-9EB7809EC588F2D7
Descriptive Methods for the Examination of Wormholes and Black Holes - Presentation by Marcus Baumgartl (Munich University) about wormholes, their description within general relativity (including Penrose diagrams), and their role for time-travel. - http://www.theorie.physik.uni-muenchen.de/~marco/poster/1.html
White Holes and Wormholes - Illustrations of White Hole and wormhole geometry, plus a visualization of what the view through a wormhole would look like. One of Andrew Hamilton's excellent pages about visualizing relativity. - http://casa.colorado.edu/~ajsh/schww.html