XBee modems are one of the easiest ways to create a wireless point-to-point or mesh network. They have error correction, are configured with AT commands, come in multiple flavors and can create a wireless serial link out of the box! I wanted to make a wireless Arduino project but all the adapter boards on the market made me unhappy. So I designed what I think is an excellent low-cost adapter board.
An XBee wireless modem adapter - [Link]