Arduino 433Mhz RF Wireless Data Transfer
Here is a tutorial on how to use 433MHz RF modules to send data from an Arduino to another. The example code transmits a message to the serial port of receiver.
The most practical and cool way of sharing data from 1 Arduino to another is by far using a radio transmitter and receiver. The simplest form of wireless transmission (I could find) is the 433Mhz ASK modules. They come in pairs, a receiver and a transmitter. They are ridiculously cheap, selling at $1 or less a pair!!
Arduino 433Mhz RF Wireless Data Transfer – [Link]