PostLBS is an opensource toolkit that utilizes PostGIS to do routing and location based services. Common classes of problems solved by it are Shortest Path, Driving Distance and Traveling Salesman. PostLBS is a project funded by Orkney, Inc.
David Techer provides a well diagrammed and thought out tutorial on installing and using PgRouting to calculate itineraries. Unfortunately its in French, but nevertheless still useful since its so well diagrammed even if you are not a French speaker. Check out David Techer's routing tutorial at PgRouting tutorial
For English Speakers - the Google automated translation - PgRouting tutorial Google English