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