Here’s an oft-overlooked search engine that you may want to take a look at. A9 is currently using Google for its web search, but it has got built-in book search as well. It searches the entire text of a huge library of books digitized by Amazon.com. So it’s a tool for mining for online and offline information.

A closer look shows some real innovations in personalization integrated with search:

• A9 remembers your past searches and displays them on the home page.
• A9 remembers results that you have clicked and when, annotating future results (e.g. “clicked 3 hours ago”).
• and the A9 toolbar maintains visited page history.

(Note that you must be logged in with your Amazon.com login to access of all A9’s personalization features.)

Each search result has “Site Info” with quick access to Alexa data (which includes traffic history, sites that were also visited by those who visited the site in question, and other metadata).

And… this one was a surprise… the toolbar can be used to annotate web pages as you visit them. Your notes are immediately and automatically saved, and they’re available from any other computer simply by logging in to A9 and having the A9 toolbar installed.

A9 also allows you to virtually walk down the block in a handful of major cities in the US. They actually took a bunch of trucks armed with cameras mounted on them and took pictures of the façade of each of these businesses. So you can type in a street or the name of a business and you can actually see what it looks like from the street. They have done this in New York City, San Francisco and more. That’s pretty cool!

I think A9 is one to watch… Consider installing A9’s toolbar and using A9 as your default search engine to get a glimpse of A9’s potential. And if they personalize search rankings for users as I imagine they will, things could get very interesting.

UPDATE: A9 has switched from using Google for web searches to MSN Search