The Arizona Cardinals and Philadelphia Eagles secured their places in the postseason while last season's Super Bowl champions Pittsburgh kept their slim hopes alive with a last-gasp win over the Green Bay Packers.
"It's definitely sweet considering how we started the season," cornerback Quentin Jammer told reporters.
San Diego lost three of their first five games but have now won nine in a row and improved to 17-0 in December since 2005.
The Bengals had hoped to win the game as a tribute to Henry, who died from injuries suffered in a fall from a pickup truck after a "domestic situation" with his fiancee, police said.
"It was sort of like an empty feeling and I think a lot of people don't understand," said the Bengals' Chad Ochocinco.
Arizona and Philadelphia joined the Chargers in the postseason, taking NFC berths, while the already-playoff bound Minnesota Vikings (11-3) won the NFC North despite a 26-7 loss to Carolina.
The Cardinals (9-5) defeated the Detroit Lions 31-24 and were crowned NFC West champions when the Philadelphia Eagles (10-4) eliminated the San Francisco 49ers with a 27-13 victory.
The Eagles' win, their fifth in a row, assures them of at least a wild-card spot. They lead the Dallas Cowboys by a game in the tight NFC East race, with two games to play.
Minnesota clinched the NFC North when the Pittsburgh Steelers scored on the final play of the game to defeat the Packers 37-36.
The Steelers are one of six AFC teams with 7-7 records still in the hunt for a wildcard berth, the league said on their website (www.nfl.com)
The unbeaten Indianapolis Colts (14-0) of the AFC and the NFC's New Orleans Saints (13-1) have also secured playoff spots and both have clinched first-round byes. (Reporting by Gene Cherry in Salvo, North Carolina)