1. Use a Search Engine. The bane of librarians everywhere, Google, and other search engines like it, is one-stop shopping for information. Remember that adding search terms adds specificity to your search - think a little deeper into your topic to locate the information you seek. Also, don't forget that placing quotation marks around your query forces the search for that exact phrase, instead of just the terms occurring somewhere (not necessarily together) in the document. For a more scholarly search, you can try Google Scholar.
2. Use a Web Directory. If Google isn't getting you where you need to go, or you'd like to review a list of sites that pertain to your topic, use a directory. Directories are human-created indexes of the Internet. Here's Yahoo's, Google's, and here's DMOZ (which is user-created and really neat.) The thing that makes a directory different, and some would say better, than a search engine is that you can read a short preview of the entire site - not just the page - from the list. Also, when you simple do a typical "web search", it will find many pages that pertain to the phrase you entered - but not necessarily the topic. Directories are focused on the topic, and therefore organize the web better.
3. Use Printed, Online, or Human Resources. Journals and educational magazines will often mention useful sites, but don't forget that other teachers, professors, and your librarian can be a great source also. Actually, while you're down at the library, ask your librarian what online resources the school pays for. Your district probably pays a fee for access to online information that is not available to the general public. Don't let these go to waste!