Inexpensive medium-range wireless for small projects
Here is a Chinese el-chepo version of the Xbee, for US$3.70 on DealExtreme. Free shipping to most countries.

It is a module, so it should be a plug and play just like the Xbee. Uses simple serial to communicate. The only let down is that these things (nor any other electronic modules on DealExtreme) are not well documented on the site. Hunt around for a datasheet.