ThrustHP is nice, but does me no good at the field. I made a small spreadsheet which I uploaded to my Palm Pilot so I can get insight into different props at the field.

You can play with Excel's Solver if you like to see what RPM you should be at for a given RPM; in it's current layout, you can see if you are under-propped based upon the horsepower of the engine and the prop used. You can also check pitch speed as well as total Watts used.

http://www.flindt.us/planes/prop_performance.xls