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