Formal/Official:
* Announced
* Proclaimed
* Pronounced
* Published
* Stated
* Affirmed
* Asserted
* Averred
Informal:
* Said
* Spoke
* Noted
* Made known
* Revealed
Specific to specific situations:
* Declared war - Launched
* Declared bankrupt - Insolvent
* Declared a winner - Proclaimed
The best synonym for "declared" will depend on the specific context of the sentence.