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