What's new / key features

18 Megapixel C MOS sensor. The EOS 7D sports a new 18 MP APS-C CMOS sensor which is an in-house development. Canon claims the sensor delivers an improved signal to noise ratio which is achieved through a new photodiode and microlens design. The EOS 7D's sensor features the gapless microlenses that we first saw on the EOS 50D but on the new model the distance between microlenses and photodiodes has been reduced which results in the light being more easily focused onto the photodiode.
New 19-point AF system. The new AF-system features 19 cross-type sensors and is highly customizable (see below for details). You can even specify a different AF-point selection mode and selected point (or zone) that the camera should jump to, depending on its orientation (Landscape, Portrait grip up, Portrait grip down). This makes use of the accelerometers used to provide the level display.
Viewfinder. The 7D is the first EOS camera with a 100 percent coverage and 1.0x magnification viewfinder specification. A transmissive LCD in the viewfinder displays AF points, spot metering circle and composition grid. 3 inch Clear View II LCD. On the new 3 inch, 920K pixel screen Canon has removed the air-gap between the LCD’s protective cover and the liquid crystal to reduce glare. The screen has a viewing angle of 160 degrees. Like on the EOS 5D Mark II there is also an ambient light sensor for automatically setting the most adequate brightness for the light conditions. 
Metering system. The new Focus Color Luminance metering system (iFCL) measures focus, color and luminance across 63 zones.
Custom Controls. The new custom controls interface in the custom functions menu allows for near-endless customization of buttons and controls. The location of the controls is highlighted on a schematic depiction of the camera. Dual Axis Electronic Level. The electronic level shows both pitch and roll angles. It can be displayed in the viewfinder using the AF point indicators or on the LCD and uses the same acceleration sensor as the 'orientation-sensitive' AF-system.
New Flash and Wireless Flash Control. The 7D is the first Canon EOS to come with an Integrated Speedlite Transmitter. The system allows to control up to three groups of four flashes each. With 15mm the built-in flash features wider flash coverage than previous models. Its guide number is 12/39 (ISO 100, in meters/feet).
Environmental Sealing. The camera comes with weather sealing that is apparently equivalent to the EOS 1N (launched in 1994, remember?). The red color on the illustration means sealing, green shows strengthened seams on the magnesium body. Dual DIGIC 4 processors provide the processing power that is needed for eight frames per second continuous shooting at all file types and image qualities.

New movie features. The 7D's movie mode features full manual control over shutter speed and aperture. Images can be recorded in 1080p resolution at 30 (NTSC), 25 (PAL) or 24 frames per second and in 720p mode with 60 (NTSC) or 50 (PAL) fps. There is also an option to cut the beginning and end of a movie in one second increments in the camera.

For easier operation there is now a dedicated switch to change from other shooting modes to movie mode. Still images can be taken at any time by pressing the shutter button and stereo sound can be recorded if an external microphone is connected.

Autofocus point selection

The 7D receives a new AF system that not only offers more AF points but also a variety of new ways of selecting them.

In addition to the standard Canon options of automatically or manually selecting AF points, the 7D gains a series of extra modes to make the most of those 19 AF points. Which of the five options are available is determined via Custom Function III. 6
Spot AF uses just the central section of each AF point to give more precise focus when using telephoto lenses (at the risk of slower focus acquisition). AF point expansion is used to aid focus tracking and will consider the points adjacent to the manually selected AF point.
Zone AF groups the points into 5 zones to concentrate the camera's attention on the part of the frame you wish it to focus on. You can also specify which point selection mode (and which point or zone), you want the camera to jump to, depending on the orientation of the camera.