Multiple Node RF Network

I would like to create a sensor network with multiple sender nodes and a single receiver. I need to have this wireless, so ethernet is out. Other than XBee, Bluetooth, or Wi-Fi, is there a simpler RF solution that will work?

What I am not sure of is how the receiver will be able to separate the data sent from the multiple sources. All of the examples I have found have been point-to-point.

Look at this site: Follow the links at the top. I've been following the guy for some time and he's created a platform like you describe. I cannot point to a more specific information as almost everything he's done is about multinode RF network based on Arduino compatible devices and code.