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