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
Earned level 40
Completed all missions in the Rust Commons
Killed the Vault Boss
Discovered Eridian Promontory
Discovered Crimson Lance Enclave
Killed Flynt
Killed the Rakk Hive
Discovered Trash Coast
Earned level 30
Earned $1,000,000
Killed 15 enemies with the Hunter's action skill
Killed Krom
Discovered Krom's Canyon
Discovered The Scrapyard
Reached proficiency level 10 with any weapon type
Completed 5 missions in the Rust Commons
Killed 25 enemies with corrosive weapons
Mastered the technology of Pandora
Completed all missions in the Arid Badlands
Killed 25 enemies by ramming them with any vehicle
Earned level 20
Equipped a class mod for your character
Killed Sledge
Discovered Headstone Mine
Killed 25 enemies with shock weapons
Killed 25 enemies with explosive weapons
Applied an elemental artifact
Discovered Sledge's Safe House
Killed 5 Rakk in under 10 seconds
Sold 50 guns to a shop
Earned level 10
Killed 15 enemies with the Soldier's action skill
Killed 25 enemies with incendiary weapons
Earned level 5
Discovered Skag Gully
Completed 5 missions in the Arid Badlands
Kill an enemy by stomping on its head
Race around the Ludicrous Speedway in under 31 seconds
Earn level 50
Win an arena match
Win a duel against another player
Rescue a groupmate from death in a co-op game
Complete 15 missions in co-op
Defeat the Rakk Hive, the Vault Boss, Sledge, Krom, or Flynt in a co-op game
Play in a co-op game with either an employee of Gearbox or someone who has this achievement
Win a duel without taking damage
Rescue enough Claptraps to earn 42 inventory slots
Kill 15 enemies with the Berserker's action skill
Completed the "Braaaaaaaaaaaaains!" mission
Killed Ned. Again.
Killed Ned...sort of
Completed the "Jakobs Fodder" mission
Completed the "House of the Ned" 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
Destroyed a Lancer while in a Racer
Killed each of the loot midgets
Destroyed the Lance Depot
Rescued Athena
Built the New Car: Monster
Kill Crawmerax the Invincible
Reach Level 61
Complete all missions in Secret Armory
Pay for a worthless tour of the world's largest bullet
Reach Level 51
Completed Tannis' crazy request
Collected 5 3D glasses
Find all 6 Claptrap Statues
Kill General Knoxx-Trap
Kill Commandant Steele-Trap
Kill Dr. Ned-Trap
Kill the INAC
Find 25 oil cans
Collect 15 claptrap bobbleheads
Collect 3 panties, 5 fish in a bag, and 15 pizzas