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