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