General synonyms:
* Happy
* Joyful
* Delighted
* Pleased
* Cheerful
* Content
* Elated
* Thrilled
* Jubilant
* Overjoyed
More specific synonyms:
* Relieved: If you're glad because something negative was avoided.
* Satisfied: If you're glad because something is complete or good enough.
* Enthusiastic: If you're glad and excited about something.
* Grateful: If you're glad because someone did something nice.
More informal synonyms:
* Tickled pink
* Over the moon
* In seventh heaven
The best synonym to use depends on the specific situation and the emotion you want to convey.