What's the best camera for wildlife and landscapes?
The best? just simply "the best", without any qualifiers, such as cost/budget?
Well, then, if you're looking for a camera body that will serve double-duty as both a wildlife camera and a landscape camera, I think you'd have trouble beating the Canon 1Ds Mark 3. If you were primarily shooting landscapes, then a medium format camera (featuring either film or a digital back) would undoubtedly be a better choice. But a medium format camera would be a hard way to go for wildlife, due to the absence of available lenses in the longer focal lengths.
Why the 1Ds III? Well, it has a full-frame sensor. This means that the "negative" is larger than that of most digital SLR cameras. This allows for the 21 megapixels, which provide excellent resolution even if you have to crop a bit to better compose the image. The large sensor also means that you fit more image (field of view) into the frame, at approximately the same resolution per subject area that cameras with smaller sensors will provide. This is a decided advantage when shooting landscapes and scenics.
Another advantage that this camera has is it's durability. This body is extremely well sealed against dust and moisture. You can take it out in the duck blind, or take it along on a dusty pack-in trip with mules and horses. It is built like a tank!
The autofocus mechanism on this camera is excellent. If you set it in AI mode, it will lock in on an incoming Mallard and maintain focus on the bird the entire time you're tracking it in the viewfinder - provided you have the hand-eye coordination to keep the active focus point on the duck. The focus mechanism is extremely fast to find and lock in on a subject, and with wildlife, often the mere fraction of a second delay will mean a missed shot.
Lastly, it will have a large library of lenses available. Many folks recognize Canon as offering the finest selection of lenses for professional grade digital SLR cameras. You won't outgrow this camera body simply due to the broad selection of tremendous lenses available for it.
If the question had been, "What is the best camera for wildlife?", I could make a case for the Nikon D700, or the Canon 1D Mark 3. But for double-duty as a wildlife and landscape body? In my opinion, the 1Ds Mark 3 is the finest choice.
PS: No, I don't own one of these cameras. They're costly ($7000), and I think my money is better spent by getting a very good camera and excellent lenses, as opposed to an excellent camera and very good lenses.