I have a few Noisli white-noise mixes that I alternate through, mostly combinations of rain, wind, and brown noise (gaussian frequency distribution). Hate the coffee shop noises. On top of that I sometimes add in music at a low volume, preferably something without lyrics, like classical or postrock. For classical I like Brahms and Schubert. Occasionally I'll mix in something atonal/arhythmic like Philip Glass or Brian Eno.