Hera are a few I know:
*#0*# Service mode, lets you check if all the Hardware is working properly
*#7353# does pretty much the same thing (a few more options than service mode)
*#1111# software version
*#2222# hardware version
Try 'em out!
Edit: Forgot to tell you that some carriers do block this stuff. So it works best on an unlocked and un branded device.
The temperature shown by dialing *#0228# is the battery temp. and not the CPU temp BTW.
Sent from a Galaxy far far away....
I would Love to change the world, but they won't give me the Source Code