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