A college introduced me to this product today, the Watchdog 15. a small self contained monitoring solution for small server rooms and data closets.
http://www.itwatchdogs.com/DataSheets/WatchDog15%28P%29_Datasheet_%2820120822%29.pdf
I have not used these, but i thought i would share. I may pick one of these up for a customer who has a large number of IDF closets around and no managed APC unit to buy the dongle to monitor temp.