There are 50 of them, and only four of them are secret. There may be spoilers in the list below so read with caution.

Presumably, these are the PlayStation 3 Trophies for the game as well, but sometimes there are slight variations so I am hesitant to commit.

• Rude Awakening (10 points) - Re-Enter the Animus.
• No Good Deed Goes Unpunished (20 points) - Open the Temple Door and learn Desmond's fate.
• Mystery Guest (20 points) - Complete Sequence 1 & 2.
• How D'ya Like Them Apples (20 points) - Complete Sequence 3.
• Heroes are Born (20 points) - Complete Sequence 4.
• The Day the Templars Cried (20 points) - Complete Sequence 5.
• Tea is for Englishmen (20 points) - Complete Sequence 6.
• The Whites of Their Eyes (20 points) - Complete Sequence 7.
• Caged Wolf (20 points) - Complete Sequence 8.
• Two if by Sea (20 points) - Complete Sequence 9.
• Grim Expectations (20 points) - Complete Sequence 10.
• Difficult End (20 points) - Complete Sequence 11.
• The Sum of Truth (50 points) - Complete Sequence 12.
• Perfectionist (50 points) - Complete 100% of all main mission constraints.
• An Extraordinary Man (10 points) - Complete the Encyclopedia of the Common Man.
• Patent Not Pending (10 points) - Craft one of Franklin's inventions to decorate your Manor.
• House Party (10 points) - Recruit any of the Artisans and see them settled on the Homestead.
• A Complete Set (20 points) - See all the optional characters settled at the Homestead.
• Original Gamer (20 points) - Win a game of Fanorona, Morris and Bowls on the Homestead.
• Bring Down the House (20 points) - Explore Fort Wolcott.
• Kidd Gloves (30 points) - Uncover the mystery of Oak Island.
• All Washed Up (40 points) - Complete all Naval Missions aboard the Aquila.
• Entrepreneur, not Pirate! (20 points) - Complete all 12 Privateer Contracts.
• Tumblehome (10 points) - Upgrade the Aquila.
• By Invitation Only (20 points) - Be invited to join a Club.
• In Good Standing (30 points) - Complete all challenges for any of the Clubs.
• Man of the People (20 points) - Liberate all districts in Boston OR New York.
• Monopoly Man (10 points) - Send a convoy to Boston, New York and the Frontier.
• Blowing in the Wind (20 points) - Retrieve every page for one of Ben Franklin's Almanacs.
• Completionist (50 points) - Complete ALL progress tracker grid entries.
• Multitasking (20 points) - Complete 50% of the Progress Tracker entries.
• Spit Roast (20 points) - Perform a double assassination using a musket.
• Circus Act (10 points) - Kill 15 guards with a single cannon shot.
• Predator (10 points) - Hang 5 enemies by using rope darts.
• Prince of Thieves (10 points) - Loot a convoy without killing any of its guards.
• Whit's fur ye'll no go by ye! (10 points) - Block a firing line 5 times by using a human shield.
• Jager Bomb (20 points) - After becoming fully Notorious, kill 10 Jagers before losing your notoriety.
• Magna cumLaude (20 points) - Have a Trainee reach the Assassin Rank.
• Coureur des Bois (10 points) - Exchange undamaged pelts at all different general stores.
• Eye Witness (10 points) - Witness a predator killing an enemy.
• Fin (30 points) - Complete each of the epilogue missions unlocked after the credits roll.
• Abstergo Entertainment (10 points) - Reach level 20 in the multiplayer mode.
• Hunter/Killer (20 points) - Reach sequence 10 in a map on Wolfpack multiplayer mode.
• Winning Team (20 points) - Be on the winning team at the end of a multiplayer game session.
• Personalized (10 points) - Customize your multiplayer Profile and Character.
• The Truth Will Out (20 points) - Unlock a hacked version of one of the Abstergo videos in the story quest.
• Four Secret Achievements

Thanks to Mike Bendel for the news tip!

[via Exophase.com and Xbox360Achievements.org]