What brand of ND filters do you have?

[wickidwombat]

Why do you say Cokin does not? Any particular reason. Is having resin instead of glass a bad thing?

No, resin isn't a bad thing.  They're lighter and less likely to break, but more likely to get scratched. 

Cokin filters are known for their color cast issues.

I think they also noticably soften the image too especially if you are using very good glass its easy to see the degredation in image quality even on the camera screen

rather than use graduated nd filtes i prefer the black card approach or rather i have a black lens cloth in my bag which i dangle over the top of the frame to reduce the sky exposure

I have the schnieder 82mm 10 stop that neuro recomends as well as a 52mm B+W 10 stop for use with my 20mm voigt and 40mm f2.8 in my light and compact kit

[RobertG.]

I use the HiTech filters for a while now. They do the job but they are definitely not the best you can get. They are rather cheap and you can see why. I've got a full set of grad and reverse grad nd filters as well as the orignal and the new 3.0 ND filter. While the newer 3.0 ND filter is a significant improvement, the strong blue color cast is still bothering me a lot.

If you are really serious into landscape photography, consider buying the Lee filters. The HiTech filters will help to save money but detoriate your image quality.