Class for DHT11, DHT21 and DHT22 (temperature & humidity)

Hi Rob,
Thank you so much for writing such an easy to use library!
I wanted to ask you a question if I may -
I'm using the DHT-11,
I tried supplying it with different voltages (3V, 3.3V, 5V - using the
Arduino Uno's 3V,5V and the Arduino Fio's 3.3V power supply)
and for each voltage there are different readings for the temperature and humidity (a
very big difference between 3V and 5V).
what is the correct voltage that it should be supplied with?
(or is there a way to work around this?)
according to the datasheet it can be supplied with 3V - 5.5V.

thanks!