I changed the sound of the lockscreen, it's based on filedeployer from HEATHCLIFF74 so all credits to him, more info HERE.
For unlocked devices only.
How does it work,
Just install the xap LockscreenSound, and after installing your sound is changed, no reset needed.
You can also remove the program from the list but the sound will not revert back to original, if you don't like the new sound and you wanna go back to the original just install the xap LockscreenSoundorg and everything is back to normal.
If you have other sounds you wanna use, just let me know and I change the xap for you.
Added i-lockscreensound, thanks to bernarduk09
Added StarWarssound, thanks to sumeet.manghnani (unlock = Lightsaber & lock = Darth Vader Breathing)