Great compilation! I listen to maybe half of these already, but curiously not while working generally. I especially like Emancipator, Tycho, Carbon Based Lifeforms, Kiasmos.
I actually didn't know about him.. i'll check it out for sure !! I actually also like to listen to piano heavy stuff.. My favorite by far is Ludovico Einaudi. My favorite albums from him is "Divenire" and "In a Time Lapse". The list should be much longer :) this was just what i could remember right off the bat.
Carbon Based Lifeforms - Tensor
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Really most CBL is good.. :) but the best albums are
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World Of Sleepers
Interloper
Hydroponic Garden
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Theres also artist like
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Asura
Solar Fields
Koan
Aes Dana
Sync24 (side project from one of the CBL guys)
Ooze
Ott
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Other good artists but a bit different ambient genre would be
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Abakus (This dude is super productive and his shit is awesome !)
Kiasmos
Krusseldorf
Bluetech
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If you like your downtempo more pop then try
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Bonobo
Emanicpator
Catching Flies
Galimatias
Shlohmo
Tycho
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That was a short list on the top of my head :)