A polarizing filter is definitely my first choice for shooting nature photography with a digital camera. It has to be circular, or else autofocus won't work right.
By the way, when doing landscape work, I sometimes wear the glasses you get for 3D movies, where one lens is polarized in one orientation, and the other is polarized the other way, in order to see my options.
Last edited by Evolute; 12/15/07 04:42 AM.