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