In general, all Mitel branded phones work on the 3300. You can even use all of the DNI sets 4xxx.
But here is a listing from the PBX it self:
5005, 5010, 5020, 5140, 5205, 5207, 5212, 5215, 5220, 5224, 5230, 5235, 5240, 5330, 5340.
There are others but these are the main IP sets. Stay away from the 5201 sets and the 5302 sets.
In theroy, you can make most SIP sets work with the 3300. Think Snom.
Ralph