1.
*#06# – IMEI number
 2. *#0*# – Enter the service menu on newer phones like Galaxy S III
 3. *#*#4636#*#* – Phone information, usage statistics and battery
 4. *#*#34971539#*#* – Detailed camera information
 5. *#*#273282*255*663282*#*#* – Immediate backup of all media files
 6. *#*#197328640#*#* – Enable test mode for service
 7. *#*#232339#*#* – Wireless LAN tests
 8. *#*#0842#*#* – Backlight/vibration test
 9. *#*#2664#*#* – Test the touchscreen
 10. *#*#1111#*#* – FTA software version (1234 in the same code will give PDA and firmware version)
 11. *#12580*369# – Software and hardware info
 12. *#9090# – Diagnostic configuration
 13. *#872564# – USB logging control
 14. *#9900# – System dump mode
 15. *#301279# – HSDPA/HSUPA Control Menu
 16. *#7465625# – View phone lock status
 17. *#*#7780#*#* – Reset the /data partition to factory state
 18. *2767*3855# – Format device to factory state (will delete everything on phone)
 19. ##7764726 – Hidden service menu for Motorola Droid
Screenshot
Direct Download Links
Update x1: More codes!
 1. *#*#7594#*#* – Enable direct powering down of device once this code is entered
 2. *#*#273283*255*663282*#*#* – Make a quick backup of all the media files on your Android device
 3. *#*#232338#*#* – Shows Wi-Fi MAC address
 4. *#*#1472365#*#* – Perform a quick GPS test
 5. *#*#1575#*#* – For a more advanced GPS test
 6. *#*#0283#*#* – Perform a packet loopback test
 7. *#*#0*#*#* – Run an LCD display test
 8. *#*#0289#*#* – Run Audio test
  9. *#*#2663#*#* – Show device’s touch-screen version
  10. *#*#0588#*#* – Perform a proximity sensor test
  11. *#*#3264#*#* – Show RAM version
  12. *#*#232331#*#* – Run Bluetooth test
  13. *#*#232337#*# – Show device’s Bluetooth address
  14. *#*#7262626#*#* – Perform a field test
  15. *#*#8255#*#* – Monitor Google Talk service
  16. *#*#4986*2650468#*#* – Show Phone, Hardware, PDA, RF Call Date firmware info
  17. *#*#1234#*#* – Show PDA and Phone firmware info
  18. *#*#2222#*#* – Show FTA Hardware version
  19. *#*#44336#*#* – Show Build time and change list number
  20. *#*#8351#*#* – Enable voice dialling log mode, dial *#*#8350#*#* to disable it
  21. ##778 (+call) – Show EPST menu
Codes specific to HTC devices only:
  1. *#*#3424#*#* – Run HTC function test program
  2. *#*#4636#*#* – Show HTC info menu
  3. ##8626337# – Run VOCODER
  4. ##33284# – Perform field test
  5. *#*#8255#*#* – Launch Google Talk service monitor
  6. ##3424# – Run diagnostic mode
  7. ##3282# – Show EPST menu
  8. ##786# – Reverse Logistics Support
Note: Not all codes are supported in a phone. Try