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