Relevant info, about many crop vs. full frame comparisons: http://www.graphic-fusion.com/fullframe.htm#widetele
"Probably the biggest difference one will notice between FF and APS-C is the behavior of one's full frame lenses. When a FF lens is mounted on an APS-C camera, only a portion of the image circle is used, and the angle of view is therefore not as wide. A FF camera opens up all of the wide-angle potential of a FF lens. There is also a bit of difference in lens availability on the wide end for FF vs. APS-C. Although manufacturers have expanded their APS-C lens lines to include some extraordinarily wide angle coverage in both formats (e.g. Sigma's FF 12-24 and their largely equivalent APS-C 8-16), there are still far more lenses that will render a wide angle of view on FF cameras than on APS-C cameras. This will logically continue to be the case until such time as the APS-C wide angle offerings exceed the FF offerings by a considerable margin. If you are considering jumping into the APS-C format, just be careful that the more limited wide angle offerings are to your suiting."
Cameras with different sizes of sensors all still use the same focal length measurement. Focal length is a physical property of a lens, and is not the only factor in the field of view of an image.
For example, for a smaller-sensor sized camera (let's say Canon Powershot SD1400 IS, http://www.canon.ca/inetCA/products?m=gp&pid=3513#_030),
the focal length at the wide end of the zoom range is 5.0mm. For this camera, the FOV is a full-frame equivalent to 28mm (meaning that it is the same FOV as if you put a 28mm lens on a full-frame body). To get the full-frame equivaent FOV of 28mm on a crop (1.6x) body, the required focal length is 28/1.6=17.5mm.
No SLR lenses, to my knowledge, rate the lens in terms of equivalent (35mm) focal length.