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