In just three lines of code, you can write a web search (of sorts). You can show your users customised maps with your own special HTML-friendly markers added. You can pull in the knowledge of the world, scan the entire web and even fetch lists of items available for purchase. That’s pretty powerful. And it’s all free.

The documentation is slightly complex, and I’ve noticed quite a few developers are aware of them but haven’t bothered to take a closer look - you definitely want to examine them in detail if you’re into mashup building. Just briefly brainstorming, here are some interesting things you could achieve with the APIs:

1. Illustrating content
If you’ve got user generated content, why not use the term extraction and flickr search APIs to illustrate it too?

2. Address validation
It may not be perfect, but the APIs offer a very reasonable way to validate user-input address values.

3. Find related information / further reading
The Search APIs offer access to a massive index of the internet, covering much of the typical news outlets, the blogosphere, the wikis and, of course, the traditional content servers. Why not search the entire web to find stories documenting a particular topic or event, to provide additional information to your users?

4. Check plagiarism
When dealing with user-submitted content, plagiarism is a real problem. Users copying-and-pasting entire blocks of content can anger copyright owners and create all sorts of legal issues. Why not regularly scan the web to find sites featuring the content in your database?