A quick search suggests the utterly ubiquitous DHT11, which speaks a well documented protocol and has libraries for every conceivable microcontroller and platform. Plug that into your Arduino and ...

I’ve tried the DHT11 sensor modules at both Vcc 3.3V and 5.0V, and at both voltages the humidity values are bad. dfrobot has introduced a V2 DHT11 sensor module that changes the 10K pull-up to 4.7K.