*#06# - As mentioned in the stolen phone post, this is used to show you your Nokia E65 serial number of IMEI (International Mobile Equipment Identifier) as they call it in the mobile world.
*#92702689# (*#war0anty#) - This will show you the "Life Timer" of your phone, i.e. the total time you have spent on phone calls (in minutes). eg "Life Timer: 46:40"
*#0000# - This will show you the software version, the date when the software was built and the phone model. If you have software version 2.0633.65.01 you are up to date. If not, go here to find out how to update your phone firmware.
*#2820# (*#BTA0#) - This will display the Bluetooth device address for your Nokia E65.
Finally.. don't do this one just to try it out - it will wipe everything off your phone!
*#7370# (*#RES0#) - This will reset your phone to factory default settings. Only do this in the event of an emergency (can't think of one right now) and you don't mind losing all your customizing, which, if you are following this blog, could be quite a lot! The default security code if asked is12345.