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.
Killed an enemy with the Siren's action skill
Killed 15 enemies with the Hunter's action skill
Killed 15 enemies with the Soldier's action skill
Killed the Vault Boss
Completed all missions in the Rust Commons
Rescued enough Claptraps to earn 42 inventory slots
Killed Flynt
Killed the Rakk Hive
Raced around the Ludicrous Speedway in record time
Killed Krom
Mastered the technology of Pandora
Completed 5 missions in the Rust Commons
Completed all missions in the Arid Badlands
Killed 25 enemies by ramming them with any vehicle
Killed 25 enemies with corrosive weapons
Killed 25 enemies with explosive weapons
Sold 50 guns to a shop
Rescued a groupmate from death in a co-op game
Completed 15 missions in co-op
Defeated the Rakk Hive, the Vault Boss, Sledge, Krom, or Flynt in a co-op game
Killed Sledge
Killed 5 Rakk in under 10 seconds
Killed 25 enemies with shock weapons
Killed 25 enemies with incendiary weapons
Completed 5 missions in the Arid Badlands
Killed an enemy plumber-style
Emerged victorious from an arena match
Killed 15 enemies with the Berserker's action skill
Won a duel against another player
Won a duel without taking damage
Earned level 10
Earned $1,000,000
Applied an elemental artifact
Equipped a class mod for your character
Earned level 50
Earned level 40
Reached proficiency level 10 with any weapon type
Earned level 30
Earned level 20
I bet you never thought you'd be here.
Earned level 5
Discovered Eridian Promontory
Discovered Crimson Lance Enclave
Discovered Trash Coast
Discovered Krom's Canyon
Discovered The Scrapyard
Discovered Headstone Mine
Discovered Sledge's Safe House
Discovered Skag Gully
Gamed with fame
Completed the "Braaaaaaaaaaaaains!" mission
Killed Ned. Again.
Killed Ned...sort of
Completed the "Jakobs Fodder" mission
Completed the "House of the Ned" mission
Reached the end of the larger challenge in The Angelic Ruins coliseum
Reached the end of each of the 3 larger challenges with one character
Reached the end of the larger challenge in The Gully coliseum
Reached the end of the larger challenge in the Hell-Burbia coliseum
Completed the Prove Yourself mission
Completed all missions in Secret Armory
Destroyed the Lance Depot
Killed each of the loot midgets
Paid for a worthless tour of the world's largest bullet
Rescued Athena
Built the New Car: Monster
Reached Level 61
Killed Crawmerax the Invincible
Destroyed a Lancer while in a Racer
Reached Level 51
Collected 15 Claptrap bobbleheads
Found 25 Claptrap oil cans
Collected 3 panties, 5 fish in a bag, and 15 pizzas
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