General:
* anew
* once more
* another time
* repeatedly
* further
* still
* yet
* afresh
* over
* back
* once again
For emphasis:
* once more
* yet again
* still again
* again and again
For a sense of returning to a previous state:
* back
* reiterate
* resume
For a sense of repetition:
* repeatedly
* reoccur
* recur
The best synonym for "again" depends on the specific context of the sentence.