+1 for Naturespace. Enjoy the fact that it’s got a good variety of more traditional “white noises,” but also a broad selection of nature and ambient sounds. I do wish more of them were free, but I find the prices reasonable for the quality.

Naturespace and Rain Rain. The former for rainfall which is essentially white noise and the latter for a washing machine that covers the lower frequencies. It’s great for blocking sound if you live in a busy area.