Apart from Gazi, whom I do think as the best spin prospect at the moment:
Mosharraff Hossain - has great potential to succeed in tests, rate him higher than Sunny.
Enamul Haque Jr - not as great as I'd hoped, but good still.
Saqlain Sajib - went off the radar a bit, but bowled well even in the match where every other bowler got pwned. Do think he might do fine in the long run.