The number 16 was displayed on the doubling cube while Locke explained backgammon to Walt. This was also shown to display a 4 in the same scene. ("Pilot, Part 2")
Sayid said the transmission from Danielle had been playing for 16 years; since we know that was how long she had been in the island (and she was pregnant when she got there), we also know her daughter Alex was that many years old. ("Pilot, Part 2")
The number 16 was scribbled on the wall of graffiti when Jack went down to the hatch for the first time, along with 8, 42, and 108. ("Man of Science, Man of Faith")
The number 16 was on one of the gas pumps in Hurley's flashback. ("Everybody Hates Hugo")
Shannon said she would be working at her internship 16 hours. ("Abandoned")
Ana Lucia called in on the police radio as 8 Adam 16. ("Collision")
While Mr Eko was posing as a priest in Australia he was sent to investigate a miracle involving Charlotte Malkin. He was told by Richard Malkin that he knew it was a fraud as he too was a fraud and even accepted $16,000 from a couple in LA to tell a girl (Claire) to give away her baby. ("?")
One of the LAPD cars had the number 16 on it. ("Two for the Road")
There were 16 guns before the Others took some. When asked how many guns there are, Sawyer says, "Rifles and pistols, eleven total… In case you forgot, they took five of them right off us." ("Three Minutes")
Jack and Kate spent tense moments in the jungle, gathering firewood and breaking it into pieces, and during their angry silence and the following conversation, they broke 8 branches into 16 usable pieces. ("One of Us")
Jack pumped Desmond's chest 16 times when trying to revive him after pulling Desmond's body from the water. ("There's No Place Like Home, Part 2")
Season 5[]
The swinging pendulum in Ms. Hawking's lab passed the camera 4 times, then another 4 times (making 8). If it continued, there would be a total of 16 passes (and consequently, 15 before it). ("The Lie")
The model of the real "Jughead" bomb was EC16. ("Jughead")