I have a small server room with its own AC unit. Recently, the AC died, and the temperature increased from 70 F to > 90 F. We rarely go in this room, so I was lucky that someone happened to notice that the fans were running a lot louder than normal as they walked past the door. It looks like I need a way to be notified when the temperature in that room gets too hot.

What tools are you using to monitor the temperature in your server room? How does this tool notify you of a problem (email, SNMP, etc).

Note: I've read this question on server temperature, but I'm interested in the whole room, not just the inside of a server case.

Edit:

Thanks for all the great responses so far! Many of these products measure much more than just temperature. What else should I be looking at and why?