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