I think people give Parcells too much credit for the success Belicheck has had, and will hopefully soon stop having. Anyway...
The Bill Parcells Coaching Tree
Bill Parcells, DAL — His legacy has really taken off the last few seasons. Parcells was on Ray Perkins' staff in New York, but even more than Schottenheimer and Holmgren, he's really crafted himself. Maurice Carthon, who played and coached under Parcells, and Eric Mangini, the new defensive coordinator in New England, are both hot prospects who might expand the Parcells coaching tree within the next several years.
Bill Belichick, NE — This is the one every fan knows. Belichick was an assistant for Perkins, too, and Parcells kept him on when he became head coach. Belichick also worked for Parcells with the Patriots and Jets before returning to New England in 2000.
Romeo Crennel, CLE — Perkins may not have been an exceptional coach, but he knew how to pick 'em. The 1981-82 Giants had Parcells, Belichick, and Crennel as assistants. Crennel stayed with the Giants until 1992, then went to the Pats when Parcells came out of retirement in 1993. He also followed Parcells to the Jets before joining Belichick's staff in '01.
Nick Saban, MIA — Saban is hard to pin down, but the Parcells tree is where he fits best, having spent four years with Belichick in Cleveland. Saban got his NFL start from Jerry Glanville in Houston in the late 1980s.
Tom Coughlin, NYG — The Parcells influence is clear in the way he runs his teams. Coughlin spent three years with Parcells, including the Giants' 1990 Super Bowl campaign.
Between Schottenheimer, Holmgren, and Parcells, 20 of the league's 32 head coaches are accounted for. That's an awfully impressive résumé for those three men. The remaining trees have fewer branches.
http://www.sports-central.org/sports/2005/04/12/the_nfl_coaching_tree.php