It is important that people remember that DOF charts and lens scales are based on some assumptions regarding viewing distance, print size and etc. The results should be considered a general guide only.
The Cambridge in Color tutorial appears to be a good source, I also have a DOF calculator and tutorial at:
DOF Table W/Definitions
There is a javascript calculator there that will probably work with Windows but might not work with Mac OS X. However, for those with Excel, there is a download link there that includes a DOF chart (and other tools) that include a digital format.
http://www.fineart-photography.com/PhotoTools.xls
Finally, there is also a tutorial about usings the DOF scale on a lens barrel at:
Using DOF Scales
It should be noted that on a lens designed for 35mm the scale will not strictly apply to a digital sensor that is smaller than 24mm x 36mm. DOF charts assume that for any given focal length the same size print will be made no matter the format. In other words, the smaller the format, the more it has to be enlarged and, consequently, focus become more critical.
In looking at DOF charts for different formats it might appear that digital cameras are at a big disadvantage DOF wise. However, a digital camera can capture the same scene with a shorter focal length than the film formats and DOF is greater for shorter focal lengths.