all modules that use the field api module
You can find all the info to format fields in the field API

If you want to know how core modules implements the Field Api, you have to enter in every hook info page and there you will find the modules that implement this concrete hook. You can also follow the links to see the code.
Here an example of hook_field_delete and the location on web page:




On the other hand, if you want to know what contributed modules have implemeted the field API, you will have to look in the contributed modules page and make a filtered search with core = 7.0 and module categories = Fields.