Drop shadow

Does anyone know how, or where a tutorial could be found showing how to create a nice drop shadow? I’ve read the tutorial on this site but I’d like to have it be a gradient. I’ve been messing around with it for a while now but my upper right edge and lower right and left corners still look weird (not smooth).

An example of exactly what I’m looking for can be found at http://www.marklearst.com. Thanks for any input.