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