This 35mm tilt-shift lens was developed for the Canon FD mount, but I have adapted it to Canon's modern EF mount by using Ed Mika's fantastic conversion kit created specifically for this lens. Copies of this lens can be found on eBay, though it isn't much cheaper than a second-hand version of Canon's modern TS-E 24mm f/3.5 lens (version 1).
Since this lens is mounted using an adapter, there is no camera control of the aperture or auto-focus. An "AF-confirm chip" built into the Ed Mika adapter provides EXIF data (focal length and maximum aperture), and enables the camera's "AF confirmation" light that lets you know when the image is in focus. However, best focus is achieved using 5x or 10x zoom in Liveview mode.
As a normal 35mm lens, the performance is very nice, but it's when you use the tilt and shift features that it really begins to shine. You can shift in order to capture photos of tall buildings, without tilting your camera upwards, which allows parallel lines to stay parallel (the building doesn't end up looking like it's falling over). You can tilt the focal plane to extend your depth of field (e.g. have everything from very close ground to distant mountains in focus at a modest aperture like f/5.6), or to shrink it (for example, for "fake miniature" photos).