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.
Collected 20 Vault-Tec Bobbleheads
Collected 10 Vault-Tec Bobbleheads
Reached Level 20 with Good Karma
Kill all the Super Mutant Behemoths
Hacked 50 terminals
Reached Level 20 with Bad Karma
Won 50 Speech Challenges
Completed "You Gotta Shoot 'Em in the Head"
Completed "Strictly Business"
Reached Level 14 with Neutral Karma
Completed "The Nuka-Cola Challenge"
Reached Level 14 with Good Karma
Completed "Head of State"
Completed "Trouble on the Homefront"
Completed "Reilly's Rangers"
Discovered 100 locations
Completed "Those!"
Completed "Agatha's Song"
Completed "Stealing Independence"
Completed "Tenpenny Tower"
Reached Level 8 with Bad Karma
Reached Level 8 with Neutral Karma
Completed "Oasis"
Reached Level 20 with Neutral Karma
Completed "Big Trouble in Big Town"
Killed 300 people
Completed "Take it Back!"
Completed "The American Dream"
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "Rescue from Paradise"
Completed "The Superhuman Gambit"
Completed "Blood Ties"
Completed "The Wasteland Survival Guide"
Completed "The Waters of Life"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Reached Level 14 with Bad Karma
Picked 50 locks
Killed 300 creatures
Placed a grenade or mine while pickpocketing
Completed "The Replicated Man"
Completed "The Power of the Atom"
Reached Level 8 with Good Karma
Completed "Galaxy News Radio"
Completed "Following in His Footsteps"
Completed "Escape!"
Took the G.O.A.T.
Got the Pip-Boy 3000
Made one of every custom weapon
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 Neutral Karma
Reached Level 30 with Bad Karma
Completed "Who Dares Wins"
Completed "Shock Value"
Completed "Death From Above"
Completed "A Meeting of the Minds"
Completed "Walking With Spirits"
Completed "The Local Flavor"
Discovered all locations within Point Lookout
Completed "This Galaxy Ain't Big Enough…"
Completed "Among the Stars"
Completed "Not of This World"
Collected all Alien Captive Recordings