The Genesis Block's calculator does allow you to factor in changes in $/BTC conversion per month in case you sell your mined BTC immediately. Look for Conversion Increase / Month (%) under Conversion and Electricity
This calculator is inaccurate because difficulty changes every 2 weeks not every month.
bitcoinwisdom is the best imo. Also bitreturn.com is nice but it uses monthly % instead of biweekly.