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