Calculating radio tx range ?

[Satelite]

Hello :
Does anybody know of a program that would calculate the transmit range of radio signals ?
Something that the person enters the wattage/freq/db gain/rx sensitivity ect and then gives an aprox transmit range of sorts.
I realize terrain such as hills buildings metal ect would enter into this but im looking for a program that would calculate straight line of sight .
Thank you
Satelite

[citylink_uk]

A very good and free program:

http://www.cplus.org/rmw/english1.html