How can you not love these boards? They're cheap (<$2), fast, have a decent IO pin count, have low power modes and built in wifi! I will never stop using Atmega chips but for anything that might possibly be connected this is my go to chip for now.
Reading/Writing data between deepSleep
system_rtc_mem_read(64, rtcStore, 2);
system_rtc_mem_write(64, rtcStore, 2);
SDK Link: http://esp8266.ru/download/esp8266-doc/april-2015/2C-ESP8266__SDK__Programming%20Guide__EN_v1.0.1.pdf