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