Sites like Synthcloud and LFO Store offer professional "evolving pad" and ambient sound sets for download.
For the gigging musician, the ultimate setup is:
Korg 01/W sounds: Best portable/downloadable options (SF2, Kontakt, iPad)?
If you want the 01/W experience on a laptop or tablet without hauling hardware:
He closed his eyes and let the sequences run, his fingers dancing across the small portable keys, resurrecting the golden era of synthesis in the heart of the future.