(note - you will need a Google account or GMail account to use this feature)
Google Alerts are email updates of the latest relevant Google results (web, news, etc.) based on your choice of query or topic.
http://www.google.com/alerts.
It offers a lot of nifty uses:
* monitoring a developing news story
* keeping current on a competitor or industry
* getting the latest on a celebrity or event
* keeping tabs on your favorite sports teams
Once on the site you will see the following dialog box:

For this example, I want to check Craigslist for a hydraulic Press and have Google Alerts email me when any ad on Craigslist contain those 2 words.
So lets fill in the boxes:

In the first box I enter the words "hydraulic press" followed by the following: "site:houston.craigslist.org".
The phrase "site:houston.craigslist.org" tells Google that I only want to have Google search Craigslist for the 2 words "hydraulic press". If I wanted to check another web site, I would substitute a valid web site after the term "site:"
The "Comprehensive" type search will give you a lot of details.
"Once a Day" will send you an email once a day with your custom search results, if there are any.
"Email length" tells Google how many search results to email you.
"Deliver to" is where you want your search results emailed to.
After you click on "Create Alert", you will typically immediately get an email from Google with results based on their current search database. The following is a result from the above alert:
Google Web Alert for: hydraulic press site:http://houston.craigslist.org
Mills, Lathe, CNC's, Moving Shop Hydraulic Press, Grinders a lot of tools, If you are needing machine tools to make money don't pass this up you may not kick yourself but the people you ... |
Contents of small fitness center FULL HYDRAULIC RESISTANCE CIRCUIT: Leg Press, 2 Ab/Back Machine, Inner/Outer Thigh, Squat, Overhead Press, Row Machine, Bicep/Tricep, Leg Extension, ... |
To manage your alerts once you have created on, go to this link:
http://www.google.com/alerts/manage