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