I have finally given in and bought myself a good quality ND filter. I went with the Hoya NDX400 (9-stop) filter. I bought this filter as the only 2 filters I am confident of the quality with are this, and the B+W 110 (10-stop) filter, but the B+W in the 52mm size required for my kit lens is quite a bit more expensive than the Hoya. I bought the filter from Citiwide on ebay. They are a Hong Kong based ebay store, and the service was excellent. The filter was shipped the very next day after payment was made. It did take a little while to get here from Hong Kong, but I expected that.
I took the filter out for its first real use on the weekend when I went camping at Queen Mary Falls, not far from Killarney on the Darling Downs in Queensland. I took a few shots of the falls, starting off without the filter, then with the filter for a comparison. I will post up the results tomorrow. Its a beautiful area, and I will be posting a number of shots from around there over the next week or so, the previous photo of the Condamine River Head Waters is the first posted shot from the NDX400 filter, so I will post it again, just to make sure.
This filter certainly puts the cheap one I had previously to shame :) The colours are only slightly warmer than usual, but this might just be a white balance detection problem with the filter on more than colours themselves.