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