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
Killed 15 enemies with the Soldier's action skill
Killed an enemy with the Siren's action skill
Killed 15 enemies with the Berserker's action skill
Earned level 40
Raced around the Ludicrous Speedway in record time
Completed all missions in the Rust Commons
Killed the Vault Boss
Discovered Crimson Lance Enclave
Rescued enough Claptraps to earn 42 inventory slots
Killed Flynt
Completed all missions in the Arid Badlands
Killed an enemy plumber-style
Killed 15 enemies with the Hunter's action skill
Killed 25 enemies with corrosive weapons
Sold 50 guns to a shop
Killed Krom
Mastered the technology of Pandora
Earned level 30
Emerged victorious from an arena match
Discovered Eridian Promontory
Applied an elemental artifact
I bet you never thought you'd be here.
Completed 15 missions in co-op
Discovered The Scrapyard
Completed 5 missions in the Rust Commons
Killed 25 enemies with incendiary weapons
Equipped a class mod for your character
Killed 25 enemies with shock weapons
Killed Sledge
Discovered Headstone Mine
Earned level 20
Reached proficiency level 10 with any weapon type
Defeated the Rakk Hive, the Vault Boss, Sledge, Krom, or Flynt in a co-op game
Killed the Rakk Hive
Discovered Trash Coast
Earned $1,000,000
Discovered Krom's Canyon
Rescued a groupmate from death in a co-op game
Won a duel against another player
Won a duel without taking damage
Gamed with fame
Discovered Sledge's Safe House
Killed 25 enemies by ramming them with any vehicle
Killed 25 enemies with explosive weapons
Killed 5 Rakk in under 10 seconds
Earned level 10
Earned level 5
Discovered Skag Gully
Completed 5 missions in the Arid Badlands
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 Hell-Burbia coliseum
Reached the end of the larger challenge in The Gully coliseum
Completed the Prove Yourself mission
Completed all missions in Secret Armory
Killed each of the loot midgets
Reached Level 61
Killed Crawmerax the Invincible
Destroyed the Lance Depot
Paid for a worthless tour of the world's largest bullet
Destroyed a Lancer while in a Racer
Rescued Athena
Built the New Car: Monster
Reached Level 51
Collected 15 Claptrap bobbleheads
Found 25 Claptrap oil cans
Collected 3 panties, 5 fish in a bag, and 15 pizzas
Read all 6 Claptrap statue placards
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
Knoxx is at rest...finally