Is this what you're talking about when you say the 433MHz? From the description it seems like it would integrate pretty seamlessly. Though for what I'm looking for, this is quite pricey.
This looks promising, it's cheap and small.. Really sounds perfect. But how easy would it be to integrate. The information here: Arduino Playground - Nrf2401 says it can only do either send or receive at once. How much of a problem is this in most applications?
The Xbee stuff looks great. But looking at one of the tutorials on Arduino.cc it looks insanely difficult to setup.
WHAT I WANT TO DO-----------------------------------------
Really, all I want for this part of my app is to have two or more arduino boards (ideally an unlimited number, all with different IDs).
Each one of them outputs a signal with their ID.
Each one of them is constantly listening for other IDs. Preferably also be able to pickup the strength (RSSI as someone pointed out). So in the first instance, I could set it so a light on the arduino pulsed if it was close to another arduino based on the distance away - as well as outputing the ID of the sending arduino onto a small LCD display on the receiver.
What system would work best here? I don't know enough about any of the systems from the tutorials to base purchasing a set of two...
Cheers