Our preferred three-lens landscape kit for the EOS 5D Mark III starts with the EF 16-35mm ƒ/2.8L II USM, an ultrawide zoom that's popular because of its sharpness across the zoom range. You instead could choose the EF 17-40mm ƒ/4.0 USM, a lighter, more compact and less costly optic that's easier to carry in the field. The 16-35mm's ƒ/2.8 maximum aperture isn't essential for a landscape lens, as you'll generally be shooting stopped down to optimize depth of field.
For the normal-range zoom, the new EF 24-70mm ƒ/2.8L II USM would be our first choice. The very fine EF 24-105mm ƒ/4L IS USM is an alternate. It's a stop slower and thus lighter, more compact and lower priced.
For the telezoom, our first choice would be the EF 70-200mm ƒ/4L IS. Some may raise an eyebrow to this choice when Canon makes the EF 70-200mm ƒ/2.8 IS II, which is one of the highest regarded modern lenses available. The ƒ/4 version is much smaller, lighter and considerably less expensive than the ƒ/2.8 version, and if you're primarily a landscape photographer who's going to be stopping down to ƒ/16, there's almost no difference in sharpness between the two. Canon also offers 70-200mm ƒ/2.8 and ƒ/4 zooms without image stabilization, but unlike all the other lenses we recommend here, those aren't weather-resistant. If you work from a tripod and in good weather, the non-IS versions can save you a lot of money.
Sensor, Processor & ISO Range
The long-anticipated successor to the camera that started pro DSLR video mania looks to be an ideal landscape camera, too. The EOS 5D Mark III ($3,499 estimated street price) features a new 22.3-megapixel Canon CMOS sensor. That's not a huge jump over the EOS 5D Mark II's 21.1-megapixel unit, but the sensor promises a substantial increase in image quality, both still and video. A new DIGIC 5+ processor with 14-bit A/D conversion works in concert with the sensor, allowing for a normal ISO range of 100-25,600 (expandable to 50-102,400) and shooting at up to 6 fps.
A new 63-zone iFCL dual-layer metering system takes into consideration color, luminance and data from the AF system's 61 points to deliver better exposure in more situations. You also can choose center-weighted, partial (which measures the central 7.2% of the image area) or 1.5% spot metering.