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.
Reached Level 8 with Neutral Karma
Reached Level 8 with Good Karma
Kill all the Super Mutant Behemoths
Completed "Reilly's Rangers"
Made one of every custom weapon
Completed "The Superhuman Gambit"
Completed "Head of State"
Hacked 50 terminals
Completed "The Nuka-Cola Challenge"
Won 50 Speech Challenges
Discovered 100 locations
Completed "Oasis"
Completed "Blood Ties"
Completed "You Gotta Shoot 'Em in the Head"
Killed 300 people
Completed "Tenpenny Tower"
Reached Level 20 with Bad Karma
Reached Level 20 with Good Karma
Reached Level 20 with Neutral Karma
Completed "Big Trouble in Big Town"
Completed "Strictly Business"
Completed "Rescue from Paradise"
Completed "Trouble on the Homefront"
Reached Level 14 with Good Karma
Reached Level 14 with Neutral Karma
Picked 50 locks
Completed "Stealing Independence"
Completed "The Wasteland Survival Guide"
Completed "The Replicated Man"
Completed "Those!"
Completed "Agatha's Song"
Killed 300 creatures
Reached Level 14 with Bad Karma
Completed "Take it Back!"
Completed "The American Dream"
Placed a grenade or mine while pickpocketing
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "The Waters of Life"
Reached Level 8 with Bad Karma
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
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
Collected 10 Vault-Tec Bobbleheads
Collected 20 Vault-Tec Bobbleheads
Completed "Operation: Anchorage"
Completed "Paving the Way"
Completed "The Guns of Anchorage"
Completed "Aiding the Outcasts"
Completed "Free Labor"
Completed "Unsafe Working Conditions"
Completed "Into The Pitt"
Found All 100 Steel Ingots
Reached Level 30 with Good Karma
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral 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