Ned,
Those calculators are great. There are a lot of them around that do the same thing. They usually work against something called the Black-Scholes model. I have a program on my iPhone that does that. Pretty neat, calcs all the greeks for you.
What's REALLY cool is some brokers build that tool into their trading platform! ThinkorSwim's software has a tool that allows you to see expected prices on options you're looking at -- you change the date, price from current, and volatility, and it tells you what price the model would have it at.
It's a wonderful timesaver and very useful when setting GTC sell limits and figuring targets! Also, you can walk the day forward/backwards and see how time decay is affecting it.
-Dam