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