Lumicon
Astronomik
Thousand Oaks
... in that order. However Lumicon has gone through a generational change so I cannot comment on the current offering. Thousand Oaks has incredible jet black background with white nebulousity (eta carina nebula) but I feel it would benefit from a larger aperture than the 10.1" f6.4 Newtonian I was comparing with the other on.
I am also partial to the original Tele Vue O-III Bandmate filter as it is a bit broader that the three above and gives a very natural background with more stars visible but also plenty of nebulousity. This filter has now been replaced with the Type 2 version by Tele Vue in a partnership with Astronomik but I have not used the latter for comparison.
See
http://www.televue.com/engine/TV3b_page.asp?id=24