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