Absolute favorite for me too. ESP32 is now also widely available and pretty cheap for it's performance.
My second favorite ESP8266 hardware are the "Sonoff" brand WLAN mains power switches. I especially like the Sonoff S20 for its form factor, and the Sonoff POW for it's power metering capability. They contain an ESP8266 and can be reflashed with different firmware that does not need the vendors cloud services to work.
Oooh, ITEAD make sockets now? I got a bunch of switches a while ago, wrote my own firmware for them, and today I saw their wifi-enabled light switch and got one of those too. I love love love their stuff, they make it super easy to retrofit my house with "smart" devices where I can control every line of code.
My second favorite ESP8266 hardware are the "Sonoff" brand WLAN mains power switches. I especially like the Sonoff S20 for its form factor, and the Sonoff POW for it's power metering capability. They contain an ESP8266 and can be reflashed with different firmware that does not need the vendors cloud services to work.