If you have a new spoiler, please feel free to post a comment to this post. Please try to provide links and your source where applicable. They will then be added to this site.
Note: Old spoiler list here
Spoiler 1 : Jacks Tattoo will be explained in a flashback
Spoiler 2 : We will learn more about Libby through flashbacks
Spoiler 3 : We will see more of Danielle in Season 3
Spoiler 7 : Michael will only be a guest star in Season 3
Spoiler 8 : Chances to see Ana-Lucia in flashbacks are slim to none
Spoiler 10 : The island was visible for an instant on 9/22/04
Spoiler 11 : The foot statue represents the history and archeology of the island
Spoiler 12 : Kimberley Joseph is returning as Cindy in season 3
Spoiler 14 : Fake Henry was not surprised by the failsafe activation
Spoiler 15 : DHARMA = Department of Heuristics and Research on Material Applications
Spoiler 17 : This season we will learn a lot more about the Others
Spoiler 18 : There will be several new romances on the show this year
Spoiler 20 : Penny will be an important character for Season 3
Spoiler 21 : The Relationship between the outside world and the island will be explored
Spoiler 23 : The smoke creature and the monster are one and the Same
Spoiler 24 : An event will happen mid-season that will blow people away
Spoiler 25 : We will learn why Locke was paralyzed
Spoiler 26 : We will learn why Libby was in the asylum
Spoiler 27 : We will learn why the island has healing powers.
Spoiler 28 : Time may not be passing on the island at the same rate as off the island.
Spoiler 31 : Rose has a daughter
Spoiler 32 : We will understand more about the Whispers
Spoiler 35 : Jin will speak more English in season 3
Spoiler 36 : Shannon will be back in a flashback
Spoiler 39 : Jack has met one of the Others in a flashback
Spoiler 54 : Episode 7 is called "Not in Portland"
Spoiler 56 : There is more than 1 faction of Others
Spoiler 58 : The Flame Station will be found this season
Spoiler 59 : An Episode in Feb 2007 will be set mostly in London
Spoiler 60 : Juliet shoots someone twice
Spoiler 62 : Danielle's bunker was not one of the Dharma Stations
Spoiler 63 : Adam and Eve are not the Degroots
Spoiler 64 : The Others are NOT ex-hatch people
Spoiler 65 : Hurley's younger brother will feature in Episode
Spoiler 66 : Bai Ling will be appearing in Jacks flashback
Spoiler 67 : Fionnula Flanagan will be appearing in Desmond's flashback
Spoiler 68 : Kimberly Estrada to appear as Sherry in February
Spoiler 69 : Episode 11 is called "Enter 77"
Spoiler 70 : Cheech Marin will play Hurley's dad in Episode 10
Spoiler 71 : Jack is not the one shot by Juliet
OLD SPOILERS
Spoiler 4 : Desmond has join as a main cast member for Season 3
Spoiler 5 : There will be new locations inc underwater set shown in Season 3
Spoiler 6 : Michael Emerson (Fake Henry Gale) will be series regular
Spoiler 9 : We will see more of Alex next season
Spoiler 13 : Locke, Eko & Desmond are all back
Spoiler 16 : Juliet, a woman in her mid-30s, will be added to the cast as a regular
Spoiler 19 : Locke will be a very different person in Season 3
Spoiler 22 : The monster and the polar bear will be back in Season 3
Spoiler 29 : Rodrigo Santoro is the new male cast member who will play a survivor
Spoiler 30 : Elizabeth Mitchell is one of the new female cast members who plays Juliet
Spoiler 33 : Goodwin will be back in flashbacks
Spoiler 34 : Kiele Sanchez will join the cast and play Rodrigos love interest
Spoiler 37 : Jacks's wife Sarah will be back in a flashback
Spoiler 38 : Julie Adams will appear as a recurring character
Spoiler 40 : Kate possibly does not choose Saywer
Spoiler 41 : Ethan will be back
Spoiler 42 : The hatch is gone
Spoiler 46 : Boone has been seen filming
Spoiler 47 : Episode 2 has been confirmed as a Locke episode
Spoiler 48 : A new one-eyed character will be seen
Spoiler 49 : Locke has lost the use of his voice
Spoiler 50 : We will learn the real name of Fake Henry
Spoiler 51 : Rodrigo Santoro will play Paulo
Spoiler 52 : Fake Henry's name is Ben
Spoiler 53 : Episode 6 is Kate Centric
Spoiler 55 : The Sawyer and Kate kiss is not a dream
Spoiler 57 : Nathan Fillion will be joining the cast
Spoiler 61 : Kate gets married under her assumed name of Monica
Spoiler 2 : We will learn more about Libby through flashbacks
Spoiler 3 : We will see more of Danielle in Season 3
Spoiler 7 : Michael will only be a guest star in Season 3
Spoiler 8 : Chances to see Ana-Lucia in flashbacks are slim to none
Spoiler 10 : The island was visible for an instant on 9/22/04
Spoiler 11 : The foot statue represents the history and archeology of the island
Spoiler 12 : Kimberley Joseph is returning as Cindy in season 3
Spoiler 14 : Fake Henry was not surprised by the failsafe activation
Spoiler 15 : DHARMA = Department of Heuristics and Research on Material Applications
Spoiler 17 : This season we will learn a lot more about the Others
Spoiler 18 : There will be several new romances on the show this year
Spoiler 20 : Penny will be an important character for Season 3
Spoiler 21 : The Relationship between the outside world and the island will be explored
Spoiler 23 : The smoke creature and the monster are one and the Same
Spoiler 24 : An event will happen mid-season that will blow people away
Spoiler 25 : We will learn why Locke was paralyzed
Spoiler 26 : We will learn why Libby was in the asylum
Spoiler 27 : We will learn why the island has healing powers.
Spoiler 28 : Time may not be passing on the island at the same rate as off the island.
Spoiler 31 : Rose has a daughter
Spoiler 32 : We will understand more about the Whispers
Spoiler 35 : Jin will speak more English in season 3
Spoiler 36 : Shannon will be back in a flashback
Spoiler 39 : Jack has met one of the Others in a flashback
Spoiler 54 : Episode 7 is called "Not in Portland"
Spoiler 56 : There is more than 1 faction of Others
Spoiler 58 : The Flame Station will be found this season
Spoiler 59 : An Episode in Feb 2007 will be set mostly in London
Spoiler 60 : Juliet shoots someone twice
Spoiler 62 : Danielle's bunker was not one of the Dharma Stations
Spoiler 63 : Adam and Eve are not the Degroots
Spoiler 64 : The Others are NOT ex-hatch people
Spoiler 65 : Hurley's younger brother will feature in Episode
Spoiler 66 : Bai Ling will be appearing in Jacks flashback
Spoiler 67 : Fionnula Flanagan will be appearing in Desmond's flashback
Spoiler 68 : Kimberly Estrada to appear as Sherry in February
Spoiler 69 : Episode 11 is called "Enter 77"
Spoiler 70 : Cheech Marin will play Hurley's dad in Episode 10
Spoiler 71 : Jack is not the one shot by Juliet
OLD SPOILERS