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