I thought I'd do something nice, so I'm going to compile a quick batch of codes for Nokias. This is all from memory, so If I'm wrong on some of these correct me.

Nokia TDMA/CDMA:
*3001#12345# --Nam Programming
*#639# --MIN programming
*#9999# --Misc. Information
*#92702689# -or- *#92772689#--Misc. Information
*#837# --Version Information

Nokia GSM:
*#170602112302# --Software Version
*#06# --Check IMEI (Used to unlock phone)
*#746025625# --May stop SIM clock, allowing free airtime/SMS

Thats all I can think of right now, I'll try and get more up later.