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