5 out of 5 rating for Syrinscape
I've been using the Syrinscape Fantasy Player and it's great for providing an atmospheric background that you can just leave running while you GM. It's hugely tweakable, with the ability to adjust the relative volumes of individual elements (a crackling fire, distant growls, birds tweeting, etc.).
Although many of the Syrinscape sound-sets are designed for Pathfinder adventure paths, don't let this put you off it you don't run Pathfinder, or are not running the adventures in question. All sound-sets elements are usable in any fantasy campaign, and you can mix and match sounds from different sets to create your own moods (the music from the woodland set, footsteps from the dungeons set, and the sound of the sea from the shore set, for example).
There is undeniably some prep time in creating your own moods, but once you have created a few, you will probably return to them regularly. I have created a few sets for different locations in my game (specific towns, dungeon settings, rural journeys, taverns, etc.), and I use these all the time.
When a new sound-set is released, I always look forward to going through all the moods and listening out for things I can use in my own custom sets. All of the provided sound-sets are good, but some are astounding. For example: I used the sounds and music in the Siren set to build an increasingly tense series of moods as my players explored a ruined fort. As they got nearer to the siren (harpy in my game), the sinister whispers, taunts and enchanting songs got louder. By the time they encountered the harpy, my players (and me) were totally freaked out, making this an encounter we all remember.