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 20 Vault-Tec Bobbleheads
Made one of every custom weapon
Hacked 50 terminals
Completed "The Nuka-Cola Challenge"
Discovered 100 locations
Collected 10 Vault-Tec Bobbleheads
Killed 300 people
Completed "Rescue from Paradise"
Completed "Strictly Business"
Completed "Oasis"
Reached Level 20 with Bad Karma
Reached Level 20 with Neutral Karma
Reached Level 20 with Good Karma
Won 50 Speech Challenges
Completed "The Superhuman Gambit"
Completed "You Gotta Shoot 'Em in the Head"
Completed "Trouble on the Homefront"
Picked 50 locks
Completed "Agatha's Song"
Completed "Stealing Independence"
Completed "The Wasteland Survival Guide"
Reached Level 14 with Neutral Karma
Reached Level 14 with Bad Karma
Reached Level 14 with Good Karma
Completed "Head of State"
Completed "Reilly's Rangers"
Killed 300 creatures
Completed "Those!"
Completed "Galaxy News Radio"
Reached Level 8 with Bad Karma
Reached Level 8 with Neutral Karma
Completed "Tenpenny Tower"
Completed "Blood Ties"
Completed "Big Trouble in Big Town"
Placed a grenade or mine while pickpocketing
Took the G.O.A.T.
Completed "Take it Back!"
Completed "The American Dream"
Completed "Finding the Garden of Eden"
Completed "Picking up the Trail"
Reached Level 8 with Good Karma
Completed "The Waters of Life"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Completed "The Replicated Man"
Completed "The Power of the Atom"
Completed "Following in His Footsteps"
Completed "Escape!"
Got the Pip-Boy 3000
Completed "Operation: Anchorage"
Completed "Paving the Way"
Completed "The Guns of Anchorage"
Completed "Aiding the Outcasts"
Completed "Free Labor"
Completed "Unsafe Working Conditions"
Found All 100 Steel Ingots
Completed "Into The Pitt"
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral Karma
Reached Level 30 with Good 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