*#*#4636#*#* for battery and other general setttings like GSM/CDMA
*#*#8255#*#* for Gtalk service monitor 
*#*#7780#*#* for factory data reset
*#*#34971539#*#* for information about phone camera (be very careful hitting options here)
*#*#7594#*#* change the "Power" button action in your phone.
*#*#197328640#*#* service mode
*#197238640# service mode
*#0*# testing mode
*#1234# display phones current firmware
*#*#1472365#*#* gps test
*#0011# network mode/cell info/power info 
*#*#0*#*#* screen test menu
*#7465625# engineering mode
*#3214789650# gps service menu for JP3 fw
*#9900# Sysdump screen.. some sort of way to dump ram and other logs to sd card
*2767*3855# FACTORY DATA WIPE AND inteal SD RESET as soon as you enter # use only if you want wipe your phone
*#*#273283*255*663282*#*#* Opens a File copy screen where you can backup your media files


New Froyo Codes !!!

*#1234# (View SW Version PDA, CSC, MODEM)
*#12580*369# (SW & HW Info)
*#197328640# (Service Mode)
*#0228# (ADC Reading)
*#32489# (Ciphering Info)
*#232337# (Bluetooth Address)
*#232331# (Bluetooth Test Mode)
*#232338# (WLAN MAC Address)
*#232339# (WLAN Test Mode)
*#0842# (Vibra Motor Test Mode)
*#0782# (Real Time Clock Test)
*#0673# (Audio Test Mode)
*#0*# (General Test Mode)
*#2263# (RF Band Selection)
*#9090# (Diagnostic ConfiguratioN)
*#7284# (USB I2C Mode Control)
*#872564# (USB Logging Control)
*#4238378# (GCF Configuration)
*#0283# (Audio Loopback Control)
*#1575# (GPS Control Menu)
*#3214789650# (LBS Test Mode)
*#745# (RIL Dump Menu)
*#746# (Debug Dump Menu)
*#9900# (System Dump Mode)
*#44336# (Sofware Version Info)
*#7780# (Factory Reset)
*2767*3855# (Full Factory Reset)
*#0289# (Melody Test Mode)
*#2663# (TSP / TSK firmware update)
*#03# (NAND Flash S/N)
*#0589# (Light Sensor Test Mode)
*#0588# (Proximity Sensor Test Mode)
*#273283*255*3282*# (Data Create Menu)
*#273283*255*663282*# (Data Create SD Card)
*#3282*727336*# (Data Usage Status)
*#7594# (Remap Shutdown to End Call TSK)
*#34971539# (Camera Firmware Update)
*#526# (WLAN Engineering Mode)
*#528# (WLAN Engineering Mode)
*#7412365# (Camera Firmware Menu)
*#80# (Unknown)
*#07# (Test History)
*#3214789# (GCF Mode Status)
*#272886# (Auto Answer Selection)
*#8736364# (OTA Update Menu)
*#301279# (HSDPA/HSUPA Control Menu)
*#7353# (Quick Test Menu)
*2767*4387264636# (Sellout SMS / PCODE view)
*#7465625# (View Phone Lock Status)
*7465625*638*# (Configure Network Lock MCC/MNC)
#7465625*638*# (Insert Network Lock Keycode)
*7465625*782*# (Configure Network Lock NSP)
#7465625*782*# (Insert Partitial Network Lock Keycode)
*7465625*77*# (Insert Network Lock Keycode SP)
#7465625*77*# (Insert Operator Lock Keycode)
*7465625*27*# (Insert Network Lock Keycode NSP/CP)
#7465625*27*# (Insert Content Provider Keycode)

*#272*imei#* Product code , works on Froyo