Thermostat wiring schematics can be found on blogs authored by professional electricians, such as How-to-Wire-It.com or Electrical-Online.com. More generic building information sites, such as InspectAPedia.com also offer numerous schematics.
The electrician blogs tend to offer generic wiring diagrams that apply to the general type of appliance being wired. These sites offer some instruction on how to identify different electrical circuits and differences between the general diagrams and what the reader might be working on. The How-to-Wire-It.com site also includes additional instruction, such as video on how to replace a standard thermostat with a programmable one. InspectAPedia.com contains numerous schematics that are specific to each brand name and model of thermostat but doesn't offer any general instruction on identifying different types of electrical circuits.