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