Edit (21/04/2012): Please note that Astar in this is broken so go to here for my Github repo with a much faster version. I'm currently updating the Grid based sight so expect a new version in the repo linked above.
(21/03/2012) Updated. Now the action which creates the cells has an opacity range between 0 and 1. Default is 1. This controls how much opacity is used e.g. setting as 1 is 0-100 opacity drop off. Setting as 0.3 would be 0-30 opacity drop off. Experiment and hopefully it will make sense. The behavior uses inverse square to calculate the opacity using this action to create cells. For more control or to use your own equation use the crossed out code. No more black/white tiles either.
There's an example project in the zip file.
Edit2 (Quite old now): Here is the original thread I started with some examples.