My absolute favorite is mynoise.net which is an incredibly awesome sound generator. It has White/Brown/Grey/Pink/etc noise, it has Nature, Soundscapes, Atmospheres, Patternscapes, ASMR, Tonal Drones, and even Industrial noises if that's your thing. You can even customize different levels of sounds or block them out completely. You can even use it for background ambiance for boardgames.
When I've had too much of mynoise.net I go to ambient-mixer.com which is really similar, but it also has nice soundscapes from popular television and film series, like Doctor Who, Game of Thrones, Harry Potter and Star Wars, to name a few.
Aside from that, I find that listening to classical music can really help tone out nearby distractions and help me focus as well. For that I use Amazon Music Player/Google Play Music/Spotify/Youtube.
Hope either of my top two links helps someone out someday