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 "Rescue from Paradise"
Completed "Finding the Garden of Eden"
Completed "The American Dream"
Completed "The Superhuman Gambit"
Completed "Those!"
Completed "The Nuka-Cola Challenge"
Completed "Head of State"
Completed "The Replicated Man"
Completed "The Power of the Atom"
Completed "Tenpenny Tower"
Completed "Strictly Business"
Completed "You Gotta Shoot 'Em in the Head"
Completed "Stealing Independence"
Completed "Agatha's Song"
Reached Level 8 with Neutral Karma
Reached Level 14 with Bad Karma
Reached Level 14 with Neutral Karma
Reached Level 14 with Good Karma
Reached Level 20 with Bad Karma
Reached Level 20 with Neutral Karma
Reached Level 20 with Good Karma
Made one of every custom weapon
Killed 300 people
Killed 300 creatures
Won 50 Speech Challenges
Discovered 100 locations
Placed a grenade or mine while pickpocketing
Kill all the Super Mutant Behemoths
Collected 20 Vault-Tec Bobbleheads
Hacked 50 terminals
Reached Level 8 with Bad Karma
Completed "Take it Back!"
Completed "Picking up the Trail"
Collected 10 Vault-Tec Bobbleheads
Completed "Oasis"
Picked 50 locks
Completed "Reilly's Rangers"
Completed "The Wasteland Survival Guide"
Completed "Trouble on the Homefront"
Completed "The Waters of Life"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Reached Level 8 with Good Karma
Completed "Blood Ties"
Completed "Big Trouble in Big Town"
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 "Who Dares Wins"
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral Karma
Reached Level 30 with Good Karma
Completed "Shock Value"
Completed "Death From Above"
Discovered all locations within Point Lookout
Completed "A Meeting of the Minds"
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"