Originally Posted by Dieben
Nobody has mentioned lens filters!
Wanna see my 4x6 filter collection?
Lee 4x6 hard and soft grad set.
3stop reverse GND 4x6
which are kind of ironic since I usually bracket my exposures anyway and I decided while I was doing this, might as well do HDR shots.
Also B+W circular polarizer.
I also ran across this: NEW MagFilter CPL (Circular Polarizer) Filter by Carry Speed | Carry Speed Store
Probably not the best glass, but seems like a neat (and usable) idea.