Hoya 77mm Pro 1 Digital Neutral Density 64x Filter
Based in Japan, Hoya is a very popular name brand for photographic filters and they offer many quality products including the ND Pro 1 Digital Multi-Coated neutral density filter. The Pro 1 line is Hoya's top of the line and with this list of features, it's easy to see why. The ND Pro 1 Digital Multi-Coated neutral density filter offers several coatings to dramatically cut down flaring and aid in filter maintenance. This Pro 1 Digital is ultra thin, but retains front threads for stacking.
By being ultra thin, this filter allows you to use even wider than normal lenses without vignetting. Hoya has even gone to great lengths to reduce unwanted reflections by coating the inside of the filter ring with a matte black finish. The rings, however, are made of anodized aluminum which may cause galling against your lens if screwed on tightly. With a little care you may never have to worry about this filter getting stuck, but if it does it would be helpful to have a filter wrench in your bag. Filter wrenches are cheap and come in pairs in case you lose one.
As you might expect, the Hoya ND Pro 1 Digital does not introduce color casting into the image. Hoya's glass is not Schott, like the other glass filters in this list, but instead made from Hoya's own in-house glass making facility and the results are stellar.