For those wanting a good double hose regulator, as stated above, don't forget the Trieste II, and the Sportsways Hydro-Twin. Those occasionally come up on e-bay too.
The Sportsways Hydro-Twin is the 1960s equivalent of the Mentor, with a LP and HP port, and a balanced first stage. The hose/mouthpiece system should be changed out as it is too small for good air flow. It also has a mushroom exhalation valve, which is easier to maintain than the duckbills.
On the single stage side, there are still a lot of Healthways Scuba Deluxe coming onto ebay. They go for considerably less than the Aquamasters, and if you are using a steel 72 tank, they are very good regulators. They again need a different hose/mouthpiece system (USD) to perform at their best, and they have a mushroom valve exhaust rather than a duckbill valve, and so are easier to maintain.
For those who complained about the "exhalation resistance" of the New Mistral, please note that any double hose regulator will have better exhalation resistence than a single hose in normal (face down) diving positions, as the exhalation valve is higher in the water column. They also do, as Nemrod mentioned, need to be placed low on the back for optimum performance.
SeaRat
