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