I recently bought a 1-Wire serial interface (Link45) and two T-sensors from iButtonlink as well as a power injector and power adapter. The power adapter was back-ordered, but arrived today. Using a USB serial adapter and Digitemp, I get results like:
user@testmachine$ sudo digitemp_DS9097U -s /dev/ttyUSB0 -a
DigiTemp v3.5.0 Copyright 1996-2007 by Brian C. Lane
GNU Public License v2.0 - http://www.digitemp.com
Jul 06 22:26:20 Sensor 0 C: 22.81 F: 73.06
Jul 06 22:26:21 Sensor 1 C: 22.56 F: 72.61
One of the nice things is that you can add more sensors and also things like humidity sensors.
It's pretty useful. I discovered that someone had written a little plugin/wrapper for Nagios here.