Recently, while looking for a reasonably priced temperature sensor device that we could integrate into a Xymon monitoring server to monitor our server room as well as our clients' server rooms, a Google search turned up ControlByWeb.com and their 4-sensor/2-relay temperature module. It met all of our requirements.
This monitor is not only inexpensive, but it is also very simple to set up. And since the temperature readings are readily available to a web browser, it is just as easy to integrate into a Xymon monitoring server using some simple shell scripting and a great utility called "curl" to pull the state.xml web page that contains the temperature readings.
Take a look at http://www.revpol.com/xymon_cbw_temp_script to see the Xymon integration instructions and the actual bash shell script you may use to monitor, log, and graph up to four temperature reading from one of these devices.
To learn more about Xymon and some of the other Open-Source tools we use and support on our network and our clients' networks, see our System Monitoring page .
posted from my Nokia N900