The 18 contestants that competed for the coveted Biggest Loser title and the $250,000 prize were:

Lezlye Donahue, 34, Metairie, LA
Bill Germanakos, 40, Long Island, NY
Jim Germanakos, 40, Long Island, NY
Patty Gonzalez, 34, San Diego, CA
David Griffin, 31, Cedar Hill, TN
Julie Hadden, 34, Jacksonville, FL
Phil Hawk, 27, Powell, OH
Jerry Lisenby, 62, Peoria, IL
Jez Luckett, 24, Garden City, KS
Nicole Michalik, 26, Philadelphia, PA
Isabeau Miller, 21, Franklin, TN
Ryan Rodriguez, 29, Jackson Heights, NY
Hollie Self, 28, Phoenix, Arizona
Neil Tejwani, 25, Marblehead, MA
Amber Walker, 30, Houston, TX
Bryan Washington, 29, Riverdale, GA
Kae Whang, 27, Clark, NJ
Amy Zimmer, 28, Rochester, NY

The "Final Four" from left to right
Bill Germanakos, The Biggest Loser;
Julie Hadden, First Runner Up;
Hollie Self, Second Runner Up;
Isabeau Miller, Third Runner Up
(Not pictured:  Jim Germanakos, At-Home Winner)
All finalists were in fact members of Jillian's underdog "Black Team"
About 'The Biggest Loser' Season 4:

The fourth season of the popular weight loss series “The Biggest Loser,” had several interesting twists from previous years. For the first time ever, the show featured twin brothers Bill and Jim Germanakos from Long Island, New York, as well as Hurricane Katrina survivor Lezlye Donahue, and the oldest contestant in Biggest Loser history, up to that point, 62-year-old Jerry Lisenby from Peoria, Illinois.

During the exciting two-hour season premiere episode, Bob Harper (blue team) and Kim Lyons 
(red team) took a leap of faith (parachuting from a helicopter in fact) to meet the season’s contestants, but unbeknownst to them, they were not the only trainers. The season premiere featured the first of many show twists with the triumphant return of former trainer Jillian Michaels, who trained the secret black team of contestants who failed to be chosen for the blue or red teams. 

Throughout the season the show revealed the hopes and dreams that brought contestants to the show. From fitting in an airplane seat and not needing an extender belt to running a marathon with their family, some of the contestants couldn't remember the last time they weighed less than 300 pounds and others had their careers impacted by their dramatic weight. Their individual and collective stories impacted the trainers and viewers alike and is still considered by many to be the most memorable of all seasons.