In reply to pffft:
Soft grad 0.6 is all you need, and buy the screw in type, they are much easier to use, there is no light leak round the filter causing reflections like you can get with the square type.
Because its the soft grad type you don't need to be accurate where the grad line starts and don't need the ability to move the grad line up and down (the only real selling point of square filters) just make sure the angle of the line is correct by rotating the filter.
Tiffen filters tend to be nice and neutral.
Hope this helps
Dan