You can now jailbreak the final version of iOS 8 using a leaked version of "Pangu jailbreak" which was already used for iOS 7 jailbreak in past.
Here is how to Jailbreak iOS 8 Final..
NOTE: Make full backup of your device before proceeding.
1. Download and open Pangu 1.3.
3. It will prompt you to change the date of your device to JUN 2.
4. An app named Pangu will show on your home screen, tap that and your jailbreak will continue.