I have the feeling that educators will find many uses for Google's 'free' Custom Search Engine tool. Here are but a few ideas:
1] Have Google index the content of PDF, RTF, or DOC files by placing these in a web folder; and create a custom search that is limited to this folder;
2] Provide students access to a search engine set to scour specific resources that you update for specific grades/subjects/projects (e.g., general Craig Nansen's K-12 resources)
3] Add a custom search engine to your blog, wiki, or podcast page.
Do you have any other ideas?