Forget the moron in the green hat as he doesn't know his @$$ from 3rd base. The chopper is defined as a bike that has had everything non-essential to its operation cut off or removed to save weight. These bikes originated from the soldiers that came back from WWII and just could not get the adrenalin out of their system so they made their bikes as fast as possible. These bikes go by 'bobbers'. The bikes became radically modified during the late 50's, the 60' & 70's and up to today. These bikes are characterized by the extended and raked out front end and custom paint. Highly modified high horsepower motors completed the transformation. These bikes are only mass produced by outfits like Big Dog, West Coast Choppers, Orange County, Titan, and a host of others. Small operators and home built choppers and bobbers are among the finest made and highest quality as a slower pace work make the details. Chopper builders routinely use the Harley Davidson powerplant but have been known to use the vertical twin engine from Triumph, even the Yamaha XS series engine. The engine configuration is limited only by one's imagination.
http://www.chopperdirectory.com/Choppers/Builders/Chopper-Manufacturers.php
(this is just a small sample)
The only current major mainstream manufacturer I've seen is the Honda Fury. It seems to be a bike that is gaining popularity and is a nice looking bike.