^ When I was buying my Cir-Pol filter from my local shop, they said the difference was a coating on the glass, IIRC. Does anyone know if that's the ony difference between the two Hoya filters?
Since I was on a budget, I went with the normal one. So far it has produced very good results, though I've only used it one time, and it seemed to slow the camera a lot; it was a bright, sunny day yet I was forced to shoot at 1/100" most of the time. Restricted to that speed I practiced my panning
The "colour" codes represent the quality of the filter. Some have better coatings and are more flare-resistant than others, and price increases as you head towards the Pro series. As long as you get a circular polarizer (not a linear) you should be OK.