HELIOPAN OR B+W
May I suggest variable ND grads? They are very convenient to use, and while more expensive than one fixed ND filter, are probably cheaper than several. Here's a very detailed review of a few of the more popular brands: http://www.youtube.com/watch?v=nECdBiu5Rrw. Surprisingly, the relatively cheap Tiffen performs very well.
|Classic Cruisers by Surfwalker|
from Song Titles- Little Deuce Coupe
|Gosford Reflections DP by MarioSS|