[Get this Lens]
There is no debate that 50 mm is the “normal lens” for traditional 35mm SLR or full-frame DSLR cameras. However, for DSLRs with reduced sensor sizes, like the APS-C sensor in the Canon EOS Rebel line, this is not an open-and-shut case.
I think that the source of this disagreement is the actual definition of normal.
Definition-1: Normal = Same field of view as the human eye.
To compensate for the image crop effect produced with an APS-C senor, a normal lens would have scaled down to 28 mm.
Definition-2: Normal = Same perceived distances as human eye.
Irrespective of the sensor capturing the image, the lens is always producing the same image at the focus plane of the camera. The sensor-size crop effect is just reducing the final field-of-view window into this image. 50 mm is always the equivalent to the depth perspective seen by our eyes. 100 mm is 2x zoom, 200 mm is 4x zoom and so on.
The key distinction here is also the difference between digital zoom and optical zoom. With optical zoom, the actual depth perspective is affected when moving through focal lengths. The relationship between objects at different distances is never static and can make or break the final photo. This is not the case with digital zoom, which is just an image crop and expand.
The APS-C crop can be thought of as a digital zoom applied on top of the optical zoom of the lens being used in the DSLR.
To me the second definition is the one that rings truer. This means that 50 mm is always the “normal” lens, irrespective of the sensor size in the DSLR being used. If you want to capture a scene as viewed by your eyes without any additional optical zoom related perspective distortion, you need the 50 mm normal lens.
[Note: The author of the linked article makes great points regarding the merits of a normal lens. However, he uses definition-1 and recommends 35 mm with a crop sensor DSLR]