The current device, based on an Atmel AVRMega168 microcontroller can monitor up to 16 DS18x20 thermometers, with a variable logging rate of 5 to 9999 seconds. The data is displayed on a multi-page LCD display for immediate viewing as well as being sent via RS232 at 19200 baud for recording. Data is time-stamped with an optional on-board 1-Wire real time clock.
Full writeup, including Eagle sources, parts list, and operation notes is available at http://thebloughs.net/hobbies/electronics/multitherm/
12/18/07 Added Java-based graphing example to the homepage (includes source). Windows only - will need slight modifications for Linux to access the serial ports.