For music I just have MP3s saved on my laptop that I play. I don't have a Spotify account, so this works just fine for me. And every once in a while I head over to my local library and borrow new movie soundtracks to use.
As far as atmospheric sounds... I have a free account over at
www.ambient-mixer.com and have saved web links to many ambient soundtracks that I use. You can search for all manner and style of ambient sounds, and can actually build and save your own if you don't find ones that work.
This was particularly helpful when I created a ambient soundtrack to use at the Abbey of St. Markovia in my
Curse of Strahd games, where it was just a whole heap of people screaming and crying. When the groups were walking around the Abbey and saw the hundreds of mongrelfolk chained and boxed up, it definitely upped the creep factor by the constant screaming in the background.