I realize that the number of sensors and ioreg formatting varies wildly between various Macs, so I sacrificed some formatting to try and make sure that it will display all possible sensors on a given machine, and at least be legible.
This should work on most recent Macs, but if you try this script out, please post a comment stating what machine you are running -- especially if it displays any garbage on your machine, as I'd like to know so I can fix it.
Download, chmod a+x scriptname, put in your PATH, and tp -h for help.
[robg adds: I tested this, and it worked well on my PowerBook. Here's what it spit out:
$ tp -l
PowerBook G4 12" PowerBook6,4 PowerPC G4 (1.1)
45.25 HDD BOTTOMSIDE Celsius
48 CPU TOPSIDE Celsius
54.75 GPU ON DIE Celsius
0.99316 CPU CORE volts
0 REAR MAIN ENCLOSURE fan RPM
28 BATTERY Celsius
I have also mirrored the script on macosxhints.com, in case it vanishes from the above link...]

