Here is the full list of all 20 Spelunky achievements worth 400 gamerscore. It takes around 80-100 hours to unlock all of the achievements on Xbox 360.
Reached the Ice Caves.
Obtained the Ankh.
Completed the game without collecting any treasure. No shortcuts.
Played Adventure Mode 1000 times.
Completed the game in under 8 minutes. No shortcuts.
Completed 100% of the journal.
Completed the game with at least two players alive. No shortcuts.
Obtained 500000 gold.
Completed the game the hard way.
Rescued all 8 hidden characters.
Reached the City of Gold.
Rescued 10 or more damsels in one game.
Completed the game without using shortcuts.
Completed the game.
Killed 12 or more shopkeepers in one game.
Reached the Temple.
Completed 50% of the journal.
Beat the Tutorial.
Reached the Jungle.
Won the kapala from Kali.