[santix]

There's also a community-based ADS-B site: https://www.adsbexchange.com/

[sean-duffy]

I use http://360radar.co.uk, which is a small site run by (I think) just one guy, but it has the best coverage hands down for the UK. It's used extensively by military aircraft enthusiasts in the UK as it'll usually show some stuff that isn't on adsbexchange, and provides some nice features such as aerodrome and weather layers in the UI.

[zymhan]

And a subreddit about ADSB: https://www.reddit.com/r/ADSB/