Cokin P Series
UPDATE : Cokin ND filters seem to have a pink colour cast to them – http://lampertron.wordpress.com/2010/03/31/cokin-nd-filters-colour-cast/

P Series Filter Holder
I use the Cokin P series filter system with my Canon 450D, which consists of a holder attached to a adaptor ring mounted on to the lens filter thread.
Some of the advantage of the Cokin P series over the standard screw mounted filters are (as I see it);
- Holder can be swapped to different lenses without removing the filters
- Filters can be swapped without having with ease
- When using graduated filters you have the option to change the filter transition point.
The Filters
Below is a list of the filters I have;
Graduated
- Neutral Gradual Grey G2 Light (ND2) – 1 stop – x2
- Neutral Gradual Grey G2 Medium (ND4) - 2 stop
- Neutral Gradual Grey G2 Full (ND8) - 3 stop