Various examples of working with the Customize API, such as creating simple and advanced panels/sections/controls/settings. But it’s mostly PHP and doesn’t touch much on the client side of things.
This is a working example of a postmeta based customizer setting by Weston Ruter. Note that some of this code won’t transfer seamlessly to, say a custom post type scenario without some adjustments, because it hardcodes for a post type of post.
Daniel Pataki does a good job walking through a more complete tour of what you might be able to accomplish with JS driven logic.
Weston Ruter guides you on creating Customizer controls that instantly toggle on or off depending on state using client-side logic. (see related gist)
A useful starting point if you want to create a dedicated customizer setup that is separate from the default experience.
An older post by Justin Tadlock grouping some guides and articles on the customizer
And lastly two streams of resources of new guides and updates on the customizer are here:
And the Make blog covering the customizer on WordPress.org: