I've converted some of the plane dating information found in Patrick Leach's Plane Type Study into an easy-to-use hypertext flowchart. Hopefully by answering a few questions about your plane you can determine which type it is.
The flowchart starts by asking questions about the cast iron bed of your plane. I've chosen the bed as a starting point because it has many easily identifiable markings, and it probably wasn't replaced that often.
Unfortunately, many plane types share the same bed markings, so other features are also used in dating. Some plane parts were frequently replaced by their owners, or are easily separated from the plane, such as irons, cap irons, knobs and totes, and lever caps. These features are avoided where possible, along with features that appear in only some planes of a given type (i.e. frog adjustment screw).
Where possible, the flowchart uses parts that were probably replaced less often, such as frogs, depth adjustment screws and lateral adjustment levers. This approach doesn't guarantee that you'll date your plane correctly, as the flowchart can be thrown off by some hybrids. The best approach is to use the flowchart to date your plane, and then visit the Plane Type Study and Plane Feature Timeline to verify the type.
Please let me know if I can improve the flowchart. The lighting makes some of the bench plane castings look like they're made of bronze or something, but they're really all cast iron. If you find errors or discrepancies, Patrick's Plane Type Study is the final authority.
For more information, read Patrick Leach's comments on Stanley plane dating.