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