I have always had good luck with a regular old 25A red filter. That, in combination with exposing for the sky more than the land (assuming we are talking landscape shots here) has led me to get some good negatives to begin with. Here is a shot done recently, with a 25A filter. I didnt manipulate this at all out of the negative, other than to clean up the dust from the scan.

FYI, Mamiya 645e with 45mm "C" lens, Tri-X 400

This shot was Mid-Day sun.