My opinions: (opinions are like a__holes, everybody has one and they all stink

)
Brake fluid: Brake fluid is hydroscopic (absorbes water) so it is a good idea to flush the system when the fluid turns dark
Power Steering: Only if contaminated.
Coolent: Replace every two years to make sure corrosion inhibiters are fresh. I used to use a flushing product, but now I think that it is not necessary unless the coolent is contaminated or neglected
Oil: I don't think that separate flush products are necessary, particularly if you are using syn oil which has a high detergent level. I'm sure that you can find dissenting opinions on this here:
the oil board
Trans fluid: I have flushed mine twice, once by dealer, once by the home method. I don't think that it is absolutely necessary if you are dropping the pan to change the filter and part of the fluid at regular intervals. I think an external filter is a good idea also.
Axles/Transfer Case: Change at regular intervals or switch to syn lube/ ATF and change at extended intervals.
Blinker fluid: Every 3 years or 20000 left turns