Full list of all 80 Borderlands achievements worth 1,750 gamerscore. It takes around 40-50 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 30 achievements worth 750 Gamerscore.
Earned level 50
Raced around the Ludicrous Speedway in record time
Killed 15 enemies with the Soldier's action skill
Killed 15 enemies with the Berserker's action skill
Killed an enemy with the Siren's action skill
Earned level 40
Defeated the Rakk Hive, the Vault Boss, Sledge, Krom, or Flynt in a co-op game
Rescued a groupmate from death in a co-op game
Won a duel against another player
Won a duel without taking damage
Emerged victorious from an arena match
Killed the Vault Boss
Discovered Eridian Promontory
Discovered Crimson Lance Enclave
Completed all missions in the Rust Commons
Rescued enough Claptraps to earn 42 inventory slots
Killed Flynt
Mastered the technology of Pandora
I bet you never thought you'd be here.
Killed the Rakk Hive
Discovered Trash Coast
Earned level 30
Earned $1,000,000
Killed an enemy plumber-style
Killed Krom
Killed 25 enemies with corrosive weapons
Discovered Krom's Canyon
Reached proficiency level 10 with any weapon type
Completed 5 missions in the Rust Commons
Discovered The Scrapyard
Completed all missions in the Arid Badlands
Earned level 20
Equipped a class mod for your character
Killed Sledge
Discovered Headstone Mine
Applied an elemental artifact
Sold 50 guns to a shop
Killed 25 enemies with shock weapons
Discovered Sledge's Safe House
Killed 15 enemies with the Hunter's action skill
Killed 5 Rakk in under 10 seconds
Killed 25 enemies with explosive weapons
Killed 25 enemies by ramming them with any vehicle
Earned level 10
Killed 25 enemies with incendiary weapons
Earned level 5
Discovered Skag Gully
Completed 5 missions in the Arid Badlands
Complete 15 missions in co-op
Play in a co-op game with either an employee of Gearbox or someone who has this achievement
Completed the "House of the Ned" mission
Completed the "Braaaaaaaaaaaaains!" mission
Killed Ned. Again.
Killed Ned...sort of
Completed the "Jakobs Fodder" mission
Complete the Prove Yourself mission
Reach the end of the larger challenge in the Hell-Burbia coliseum
Reach the end of the larger challenge in The Angelic Ruins coliseum
Reach the end of the larger challenge in The Gully coliseum
Reach the end of each of the 3 larger challenges with one character
Built the New Car: Monster
Rescue Athena
Destroy the Lance Depot
Kill Crawmerax the Invincible
Kill each of the loot midgets
Destroy a Lancer while in a Racer
Reach Level 61
Complete all missions in Secret Armory
Pay for a worthless tour of the world's largest bullet
Reached Level 51
Completed Tannis' crazy request
Collected 5 3D glasses
Defeated the Interplanetary Ninja Assassin Claptrap
The Commandant is dead-trap
Killed Ned...again and again and again
Read all 6 Claptrap statue placards
Knoxx is at rest...finally
Find 25 oil cans
Collect 15 claptrap bobbleheads
Collect 3 panties, 5 fish in a bag, and 15 pizzas