The WiX installer itself is a good example and the source is freely available via CodePlex (WiX 3.6 Beta). Check out the WixUX project, which is the bootstrapper for the WiX 3.6 install. Another Stack Overflow question is Custom WIX Burn Bootstrapper user interface?, describing how to get started.
Or if you get the latest weekly WiX releases, the project has been renamed to WixBA. See src\Setup\WixBA
.