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Cave Story (Doukutsu Monogatari) soundtrack, composed by Daisuke Amaya.
This has to be one of the best (certainly the most famous) indie games in history.
From Wikipedia: Cave Story (???? D?kutsu Monogatari) is a freeware action-adventure video game released in 2004 for PC, designed and created over five years by Daisuke Amaya, art-name Pixel. It has been translated to English by Aeon Genesis.