We saw this yesterday at the suck-tacular C3 Expo here in New York and were pretty impressed. I'm sure the IT geeks out there already know all about this thing, but the EM 1 is an environmental sensor with its own Ethernet interface. You plug it into your network and it sense humidity and temperature as well as water levels and magnet relays. You can monitor four locations with each $600 box.
The big news is that they're coming out with a rack-mounted version with temperature and humidity sensors and that fights right inside your server rack.
Product Page [Sensatronics]