General loudness:
* Shouting
* Yelling
* Bellowing
* Roaring
* Screaming
* Hollering
* Booming
Specific situations:
* Declaiming (speaking dramatically)
* Enunciating (speaking clearly and forcefully)
* Declaiming (speaking formally and with emphasis)
* Proclaiming (speaking with authority)
* Announcing (speaking publicly and clearly)
Informal:
* Raising your voice
* Speaking up
* Talking loud
The best word will depend on the context and the intended effect.