ridewithgps.com is another. If you mouse over the elevation profile below the map, it shows grades in a pop-up bubble. You'll get different answers each time you create a route with that hill, though, because the algorithm takes the elevation change over a set distance, and unless you get the starting point exactly the same each time it will give a different result.

JB

edit: FWIW if you know the elevation change and the distance the wheels traveled this calculator will spit out the average grade for the entire climb: http://www.csgnetwork.com/inclinedeclinegradecalc.html