Is there a technical name for the colonial-looking piece that goes above an exterior door?
Answers:
You are looking for what is commonly known as a "door surrounce" They are available in kit form in several styles such as colonial, georgian, and grecian. They can also be built from scratch and are limited only by your imagination and budget.
The best place to look at the components and review your options is at your local lumber company. This is not the tme to visit the big box home improvement retailers. You need an experienced lumberman who knows the product and where to get them. They will stock a limited selection of kits, but can special order anything you need. They will have literature and brochures for you to keep and will even recommend a local craftsman to install the surrounce if you need it.
Good luck with your project.
Other answers:
Lintel?
Lintel?