In an all-day workshop on APIs and mashups, Karen Coombs of the University of Houston offered numerous examples of how libraries can enhance their catalogs and websites. Her materials can be found at http://sites.google.com/site/litapreconf2009. While I don't see school librarians doing coding in PHP and XML, I do see using some of the widgets on a library webpage and even playing around with creating really simple ones on their own. There were also interesting suggestions for linking from an online catalog to resources elsewhere (e.g., book covers in Amazon or LibraryThing), reviews, etc.
Yahoo Pipes is a simple way to find some already created mashups as well as find some and modify them to meet your needs. Try out creating a mashup from multiple RSS feeds on specific keywords.
2 years ago