First of all, you dont need a lot of airflow. Computer cases are relatively small enclosures.
120mm fan of choice: Yateloon D12SL. Does its job without being heard, or breaking your wallet.
120mm fan runner up: Evercool aluminum @ 5V.
92mm fan of choice: Panaflo M1BX @ 7V
92mm Fan runner up: Adjustable Enermax 92mm fan @ 7V or less.
80mm fan of choice: Panaflo L1A or 12L @ 9V.