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 "Finding the Garden of Eden"
Completed "The American Dream"
Completed "Take it Back!"
Completed "Head of State"
Completed "Strictly Business"
Completed "You Gotta Shoot 'Em in the Head"
Completed "Reilly's Rangers"
Made one of every custom weapon
Collected 20 Vault-Tec Bobbleheads
Reached Level 20 with Bad Karma
Hacked 50 terminals
Collected 10 Vault-Tec Bobbleheads
Reached Level 14 with Bad Karma
Reached Level 8 with Bad Karma
Kill all the Super Mutant Behemoths
Completed "The Nuka-Cola Challenge"
Completed "Rescue from Paradise"
Placed a grenade or mine while pickpocketing
Reached Level 20 with Good Karma
Completed "The Superhuman Gambit"
Completed "Trouble on the Homefront"
Completed "Tenpenny Tower"
Discovered 100 locations
Killed 300 people
Won 50 Speech Challenges
Completed "Stealing Independence"
Completed "Oasis"
Completed "Those!"
Picked 50 locks
Completed "Picking up the Trail"
Completed "The Wasteland Survival Guide"
Reached Level 14 with Good Karma
Completed "Blood Ties"
Completed "Agatha's Song"
Killed 300 creatures
Completed "The Waters of Life"
Completed "The Replicated Man"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Reached Level 8 with Good Karma
Completed "Big Trouble in Big Town"
Completed "Galaxy News Radio"
Completed "The Power of the Atom"
Completed "Following in His Footsteps"
Completed "Escape!"
Took the G.O.A.T.
Got the Pip-Boy 3000
Reached Level 8 with Neutral Karma
Reached Level 14 with Neutral Karma
Reached Level 20 with Neutral Karma
Completed "Operation: Anchorage"
Completed "Paving the Way"
Completed "The Guns of Anchorage"
Completed "Aiding the Outcasts"
Completed "Unsafe Working Conditions"
Found All 100 Steel Ingots
Completed "Free Labor"
Completed "Into The Pitt"
Completed "Who Dares Wins"
Completed "Shock Value"
Completed "Death From Above"
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral Karma
Reached Level 30 with Good Karma
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