# "Neutral Density Graduated Filters":http://www.kenrockwell.com/tech/filters.htm are a good way to get a landscape where the sun is really bright and the landscape is dark. You get something which doesn't require exposure bracketing and then processing with Photomatix to get a photo. A neutral density filter means it just makes things darker and it is darker at the top than the bottom. He uses what is called a Tiffen 0.6 which means two stops. It isn't graduated by the way, there is just a light and dark area with a line, so you ahve to line it up at the horizon. "Adorama":http://www.adorama.com/TF77CGND6X.html has them for $73 as Tiffen part number 77cgnd6.
# As an aside, if you don't have a filter like this, but do exposure bracket, the other option is to meter the sky and then meter the earth, then bracket so that you cover proper exposure for both. One will be too dark and the other too light, then use a HDR program like Photomatix to stitch it together and it will in essence use the higher exposure for the darker parts and lower for the rest. "Ron Bigelow":http://www.ronbigelow.com/articles/neutral-density/neutral-density.htm explains hot to do it manually with Photoshop.
# Get a single 77mm size filter and then buy a B+W step up ring so that you can use the same filter size. One of my lenses is 72mm and it is a pain not to have it match, so a step up ring for $12-20 is a great idea. "Adorama":http://www.adorama.com/BWSR7772.html?sid=1211864761954378 has them for $20 that is B+W part 65041214 that steps from 72mm to 77mm filter.
# Ken likes Nikon and Hoya filters the best because of the thin mounts and low prices of Hoyas. Most other folks seem to like B+W. Most folks don't like the cheaper filters like Tiffen except for graduate filters where he likes the all-glass Tiffens. You definitely by the way want multicoated and scratch resistant. One B+W lense I got was not MRC and it was scratched in 10 seconds.
"Great-Landscape-Photography":http://www.great-landscape-photography.com/graduated-filters.html has advice for square filters that you put into a holder at the front of your camera. Normally it is on a tripod. They recommend Lee filters for this purpose. The nice thing about square filters is that you can have lots and lots of them and one holder so it is cheaper since it is not really mounted on your camera. "Bob Johnson's Earthbounddelight":http://www.earthboundlight.com/phototips/neutral-density-and-graduated-nd.html makes the same comment. Use holders not screw-on filters. The most useful being two-stop soft-edged (0.6 in Tiffin talk). He likes Singh-Ray for filters.