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.
Discovered 100 locations
Killed 300 people
Completed "Agatha's Song"
Completed "The Wasteland Survival Guide"
Got the Pip-Boy 3000
Took the G.O.A.T.
Completed "Escape!"
Completed "Following in His Footsteps"
Completed "Galaxy News Radio"
Completed "Tranquility Lane"
Completed "The Waters of Life"
Completed "Picking up the Trail"
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 "Those!"
Completed "Blood Ties"
Completed "Oasis"
Completed "The Power of the Atom"
Completed "Trouble on the Homefront"
Reached Level 8 with Good Karma
Reached Level 20 with Good Karma
Picked 50 locks
Completed "Scientific Pursuits"
Completed "Stealing Independence"
Reached Level 14 with Good Karma
Completed "The Replicated Man"
Killed 300 creatures
Completed "Rescue from Paradise"
Completed "The Nuka-Cola Challenge"
Completed "Head of State"
Completed "Tenpenny Tower"
Completed "Strictly Business"
Completed "You Gotta Shoot 'Em in the Head"
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
Won 50 Speech Challenges
Hacked 50 terminals
Placed a grenade or mine while pickpocketing
Kill all the Super Mutant Behemoths
Collected 10 Vault-Tec Bobbleheads
Collected 20 Vault-Tec Bobbleheads
Completed "The Guns of Anchorage"
Completed "Aiding the Outcasts"
Completed "Paving the Way"
Completed "Operation: Anchorage"
Completed "Into The Pitt"
Completed "Unsafe Working Conditions"
Completed "Free Labor"
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 "Walking With Spirits"
Completed "The Local Flavor"
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