8 is the second of the Numbers. It is the only number which is in the Fibonnaci sequence. Below is a list of appearances on the show, by episode chronology.
8 is a very common number, and many of the occurrences could be coincidental. See article: apophenia.
While talking to Ken Halperin, Hurley had 8 instances of bad luck (shown or listed so far in the episode) when he realized the numbers might be cursed. (His grandfather died, the priest got struck by lightning at the funeral, his brother's wife left him, his mother broke her ankle, his house was caught on fire, he got arrested, an accident occured in his shoe company, a man committed suicide while he was talking with his accountant.) ("Numbers")
Aisle 8 had regular balls in Locke's store. (Aisle 15 had nerf ones, strange that the balls were kept so far apart.) ("Deus Ex Machina")
Jack and Kate spent tense moments in the jungle, gathering firewood and breaking it into usable pieces, and during their angry silence and the following conversation, they broke a total of 8 branches. ("One of Us")
The registration of the helicopter was N842M. ("Confirmed Dead")
Elsa told Sayid to meet her at the restaurant at 8:00. ("The Economist")
Jack said there were 8 survivors of the flight while on the stand at Kate's trial. ("Eggtown")
Desmond went back in time 8 years to 1996 while experiencing side effects from his travel off the island to the freighter. ("The Constant")
The expression 8mG/c4 was written on Faraday's chalkboard. ("The Constant")
Michael's passport said that he was born on July 8, 1963. ("Meet Kevin Johnson")
Miles told Michael, "80% of the people on this boat are lying about something." ("Meet Kevin Johnson")
The number 8 appeared twice on the number plate of the taxi that Ben was in when he went to visit Charles Widmore in London. (Incidentally, the car behind the taxi when it stopped had the number 8 on it.) ("The Shape of Things to Come")
The sign on the Oxford University Department of Physics was Claredon 142-08. ("Jughead")
The raft of the science expedition had 8 sides. ("The Little Prince")
There were 8 total time shifts in This Place is Death - 2 with Jin & Rousseau, 5 when the group was together, and 1 when John Locke turned the wheel. ("This Place Is Death")
Locke has suffered 8 injuries to his legs throughout the show.
1) when his father pushed him out of the window and he was paralyzed.
2) when the trebuchet he and Boone had made broke and stabbed his right leg.
3) when he lost feeling in his legs in the episode Deus Ex Machina.
4) when he purposely injured his legs to test for feeling
5) when his legs were crushed by the lockdown blast-door.
6) when he lost feeling in his legs after Ben shot him in Season 3.
7) when he was shot by Ethan during the time-flashes.
8) when he suffered a compound fracture when he fell down the well
Jack was seated in row 8 on Ajira Airways Flight 316 which departed from Gate 15. ("316")
Ben was also seated in row 8 on Ajira Airways Flight 316, as he was seated across the aisle from Jack who was in seat 8C. ("316")
Frank said he had been working for Ajira Airways for the past 8 months. ("316")
When Walt approached Locke in The Life & Death of Jeremy Bentham, two street signs were visible in the corner of the screen—one of them was "8 avenue."
There was a number 8 on the license plate of the van Ben was standing in front of when he and Sayid met in Moscow, Russia. ("He's Our You")
There were 8 video monitors in the DHARMA security room. ("He's Our You")
There was a number 8 in the ear of the rabbit statue under which Miles found the key. ("Some Like It Hoth")
Miles signed the DHARMA van back in and put the keys on hook #8. ("Some Like It Hoth")
Jacob visited 8 people off the Island who would later arrive on the Island on flight 815. ("The Incident, Parts 1 & 2")
Hugo Reyes was number 8 on Jacob's list on the cave wall. ("The Substitute")
The shipping container that held Locke was labeled 823, seen clearly on the beach after Frank mentioned Locke was "gettin' pretty ripe." ("The Substitute")
The figure eight is a popular move in ice skating.
A chess board is 8 X 8 squares.
In the Damon Lindelof-written comic book Ultimate Wolverine vs. Hulk, the Hulk is said to have killed 815 people in a New York rampage.
In Richard Adams' (author of Watership Down) book The Plague Dogs, Snitter was labeled with the number 815 in the Animal Research (Experiments on animals).
In the Film 'Back to the Future' - 88 MPH is the speed at which timetravel can occur.