*#06#
IMEI number (International Mobile Equipment Identity)

*#0000#
Firmware version and date, Phone Model and Operator Variant

*#92702689#
Life timer (W A R 0 A N T Y) - The amount of time your phone has spent sending and receiving calls.

*#62209526#
Wireless MAC Address (M A C _ W L A N)

*#2820#
Bluetooth MAC address (B T A 0?)

*#7370#
Format phone (R E S 0 ?)

*#7780#
Factory Reset (R S T 0 ?)

Note:
Format phone restores phone to as if it was out of the box. Retains firmware version and operator Variant changes but wipes all applications you have installed. Does not format the memory card so any apps on there may reinstall once powered back up again.
Another way to format some symbian phones: Power off phone. Press and hold Green, * and 3 and keep them held whilst powering on and for a few seconds after.
Factory Reset resets all settings to defaults but keeps any applications you have installed and photos etc. Both need the Security code, which, by default, is 12345.

N95 picture viewer:
2 – Scroll up (when zoomed)
4 – Scroll left (when zoomed)
5 – Zoom in (12.5%/25%/50%)
6 – Scroll right (when zoomed)
8 – Scroll down (when zoomed)
0 – Zoom out

Press and hold (in Standby):
Right selection key: Voice commands
Multimedia Key: Now Playing
1: Voice mail
2-9: shortcuts to address book you need to set up first
0: Web
#: Switches between General and Silent modes - not supported by all Operator Variants (when composing messages will switch between character and number input when held down)

12# (etc) in standby will dial the number held in location 12 on your SIM address book