I'm pretty sure the digital I/O on the ESP8266 is actually 5V tolerant according to the datasheet, though this isn't widely advertised and there's some inaccurate information drifting around from back when the specs weren't fully known. (The same isn't true of some official Arduino boards which should not be exposed to 5V on the I/O pins.) It's a very nice little chip.
to makomk: No first-hand experience, but entotheteeth on reddit, says that 5v data on the I/O will kill your device in this thread:
https://www.reddit.com/r/esp8266/comments/3bm061/5v_board_wi...
You need to run it on 3.3v which means 3.3v versions of your sensore or external level shifting. You've got limited IO compared to, say, Arduino.
But of you've got 3.3v sensors - yeah - all you need is an ESP8266 and some way of providing 3.3v. (And probably some pulldown/up resistors and decoupling caps...)