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.
Kill all the Super Mutant Behemoths
Hacked 50 terminals
Completed "Strictly Business"
Won 50 Speech Challenges
Reached Level 20 with Neutral Karma
Reached Level 20 with Good Karma
Collected 20 Vault-Tec Bobbleheads
Made one of every custom weapon
Completed "Reilly's Rangers"
Completed "You Gotta Shoot 'Em in the Head"
Reached Level 14 with Neutral Karma
Reached Level 14 with Good Karma
Completed "Trouble on the Homefront"
Reached Level 8 with Good Karma
Completed "Head of State"
Completed "Take it Back!"
Discovered 100 locations
Completed "Agatha's Song"
Completed "Stealing Independence"
Completed "Oasis"
Completed "The Nuka-Cola Challenge"
Completed "The American Dream"
Killed 300 people
Completed "The Superhuman Gambit"
Reached Level 20 with Bad Karma
Completed "Big Trouble in Big Town"
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Collected 10 Vault-Tec Bobbleheads
Killed 300 creatures
Picked 50 locks
Reached Level 14 with Bad Karma
Completed "Rescue from Paradise"
Completed "Blood Ties"
Placed a grenade or mine while pickpocketing
Completed "The Waters of Life"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Reached Level 8 with Neutral Karma
Completed "The Replicated Man"
Reached Level 8 with Bad Karma
Completed "Galaxy News Radio"
Completed "The Wasteland Survival Guide"
Completed "Those!"
Completed "Tenpenny Tower"
Completed "Following in His Footsteps"
Completed "The Power of the Atom"
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"
Completed "Into The Pitt"
Found All 100 Steel Ingots
Reached Level 30 with Neutral Karma
Reached Level 30 with Bad Karma
Reached Level 30 with Good Karma
Completed "Who Dares Wins"
Completed "Shock Value"
Completed "Death From Above"
Completed "A Meeting of the Minds"
Completed "Walking With Spirits"
Completed "The Local Flavor"
Discovered all locations within Point Lookout
Completed "This Galaxy Ain't Big Enough…"
Completed "Among the Stars"
Completed "Not of This World"
Collected all Alien Captive Recordings