With love and appreciation, I have slightly modified Mr. Brown's excellent gear calculator resource to be an "inline" javascript page with options/defaults more aimed to road bikes with double and triple chainrings.
The page defaults to have my current bike setup (compact double standard madone front ring; custom SRAM larger 10-gear rear cassette (ordered stock part that my bike store simply replaced the stock cassette with!) selected and charted below. You can click between my old bike (triple) and new bike (double) to see how similar my old and new bike ranges are! Yay -- a double that can climb so close to a triple!!)
To start "blank" click -tracey

Gear Calculator by Sheldon Brown photo Sheldon "Gain Ratio" Brown

Wheel Size
Crank Length
Gear units
Stock Cassette
Custom Cassette