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.
Kill all the Super Mutant Behemoths
Collected 10 Vault-Tec Bobbleheads
Completed "You Gotta Shoot 'Em in the Head"
Completed "The Nuka-Cola Challenge"
Placed a grenade or mine while pickpocketing
Completed "Head of State"
Hacked 50 terminals
Discovered 100 locations
Killed 300 people
Completed "Oasis"
Completed "The Wasteland Survival Guide"
Reached Level 20 with Good Karma
Completed "Agatha's Song"
Completed "Tenpenny Tower"
Completed "The Superhuman Gambit"
Picked 50 locks
Completed "Take it Back!"
Completed "The American Dream"
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Completed "Rescue from Paradise"
Completed "Trouble on the Homefront"
Reached Level 14 with Good Karma
Completed "The Waters of Life"
Completed "The Replicated Man"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Completed "Big Trouble in Big Town"
Killed 300 creatures
Completed "Reilly's Rangers"
Completed "Stealing Independence"
Completed "Those!"
Reached Level 8 with Good Karma
Completed "Galaxy News Radio"
Completed "Following in His Footsteps"
Completed "Blood Ties"
Completed "The Power of the Atom"
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
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
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 "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…"
Completed "Among the Stars"
Completed "Not of This World"
Collected all Alien Captive Recordings