Some may argue but I think the best real estate calculator and finance calculator is the HP 10BII. HP 10bII Financial Calculator
The old standby is the 12c but I cant stand RPN. HP 12C Financial Calculator
The solution here is the 12C platinum which has 'normal' algebraic entry. The platinum looks great, feels cool and sits nicely on the desk. HP 12C Platinum Financial Calculator
For ease of use and price the 10BII is the way to go for a real estate calculator. What do you use for your real estate calculator?