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