The Nordic NRF24L01+ 2.4Ghz radio board is a great little radio to use for all your projects.  No, it is not wifi compatable. It uses it's own protocal but it is very easy it integrate into an Arduino project, is low power, and is very small.  Don't let the size fool you though, it can transmit over some impressive distances. 

This article wil lgo over the basic wireing connections and an inital sketch to make sure it is working.

I replaced my closet doors and decided to also place some LED strip lighting in the closets. I look all over for a good controller to turn the LED lights on/off as the closet doors open and close.  This seemed like a simple request at first but I soon found that I didn't like any of the comercial solutions.  They all seemed to have issues.  The solution would be to build my own.  Let's face it, it's a lot more fun to build it yourself anyhow.