General:
* Shout
* Scream
* Roar
* Holler
* Call out
* Cry out
* Exclaim
* Bellow
More intense:
* Screech
* Howl
* Shrill
* Clamor
* Raucous
More controlled:
* Announce
* Declare
* Proclaim
Informal:
* Yell
* Shout
* Holler
* Whoop
Figurative:
* Thunder (used to describe the sound of a loud yell)
* Blast (used to describe a sudden, loud yell)
The best synonym to use will depend on the specific situation and the emotion you want to convey.