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