Full list of all 72 Fallout 3 achievements worth 1,550 gamerscore. It takes around 60-80 hours to unlock all of the achievements in the base game on Xbox 360.
The base game contains 50 achievements worth 1,000 Gamerscore, and there are 5 DLC packs containing 22 achievements worth 550 Gamerscore.
Won 50 Speech Challenges
Completed "Oasis"
Completed "Strictly Business"
Completed "Agatha's Song"
Reached Level 14 with Good Karma
Reached Level 14 with Neutral Karma
Completed "Rescue from Paradise"
Reached Level 8 with Neutral Karma
Reached Level 8 with Good Karma
Reached Level 20 with Bad Karma
Reached Level 20 with Neutral Karma
Completed "Head of State"
Completed "You Gotta Shoot 'Em in the Head"
Completed "The Superhuman Gambit"
Completed "Trouble on the Homefront"
Completed "Tenpenny Tower"
Completed "Stealing Independence"
Picked 50 locks
Completed "Reilly's Rangers"
Killed 300 creatures
Completed "Take it Back!"
Completed "The American Dream"
Reached Level 14 with Bad Karma
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "The Waters of Life"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Completed "Big Trouble in Big Town"
Completed "Blood Ties"
Completed "Those!"
Completed "The Replicated Man"
Completed "Galaxy News Radio"
Reached Level 8 with Bad Karma
Placed a grenade or mine while pickpocketing
Completed "The Wasteland Survival Guide"
Completed "Following in His Footsteps"
Completed "The Power of the Atom"
Completed "Escape!"
Took the G.O.A.T.
Got the Pip-Boy 3000
Completed "The Nuka-Cola Challenge"
Reached Level 20 with Good Karma
Made one of every custom weapon
Killed 300 people
Hacked 50 terminals
Discovered 100 locations
Kill all the Super Mutant Behemoths
Collected 10 Vault-Tec Bobbleheads
Collected 20 Vault-Tec Bobbleheads
Completed "Operation: Anchorage"
Completed "Paving the Way"
Completed "The Guns of Anchorage"
Completed "Aiding the Outcasts"
Completed "Into The Pitt"
Completed "Unsafe Working Conditions"
Completed "Free Labor"
Found All 100 Steel Ingots
Completed "Death From Above"
Completed "Shock Value"
Completed "Who Dares Wins"
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral Karma
Reached Level 30 with Good Karma
Completed "The Local Flavor"
Completed "Walking With Spirits"
Completed "A Meeting of the Minds"
Discovered all locations within Point Lookout
Completed "Not of This World"
Completed "Among the Stars"
Completed "This Galaxy Ain't Big Enough…"
Collected all Alien Captive Recordings