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