X-Plane. Its physics model can't be beat. (they sell a FAA certified training version based on the same engine). They have a large support base and many aircraft (fixed or rotary) which can be purchased or downloaded for free. The basic X-Plane comes with 4 helicopters, I believe.
(new - iPhone tie-in app called SkyCharts. You set X-Plane to output its path data (as if it were talking to a plotter, for instance. The iPhone thinks it's talking to a GPS) and you get real-time moving map for your sim right on the iPhone (all cont. US sectionals are included, as well as FCC airport data and IFR approach plates. Oh, and only $9.99.)
For an actual r/c flight training tool, I'd recommend RealFlight. I still think it's the top dog in r/c sims. It requires Windows, but does run very well on BootCamp. (Might evan run OK on Parallels 4, but wouldn't really recommend it.) I'm running it on XP SP3 in Boot Camp (boot native) on 17" UB MBP, though it also ran just fine on my 2.33 GHz MBP.
note: if you DO get RealFlight, it comes with a USB dual-stick "transmitter" box. X-Plane talks with it just fine and makes a nice joy-stick alternative (it has a bunch of analog knobs for flaps & brakes, plus dual/triple throw switches for other functions. Plus, it's compact and has everything in a single box.