a.js

var events = require('events');
var b = require('./b');

var emitter = module.exports = new events.EventEmitter();

module.exports.init = function(callback) {
    b.init(function() {
        emitter.emit('done');
    });
};

b.js

var c = require('./c');

module.exports.init = function(callback) {
    c.init(callback);
};

c.js

var a = require('./a');

module.exports.init = function(callback) {
    a.on('ready', function() {
        console.log('"a" is now ready! (from c)');
    });

    callback();
};

main.js

var a = require('./a');

a.on('ready', function() {
    console.log('this a.on was able to be set');
});

a.init(function() {
    console.log('finished main');
});

output

test-circular$ node main.js 

.../test-circular/c.js:5
    a.on('ready', function() {
      ^
TypeError: Object #<Object> has no method 'on'
    at Object.module.exports.init (.../test-circular/c.js:5:7)
    at Object.module.exports.init (.../test-circular/b.js:5:7)
    at EventEmitter.module.exports.init (.../test-circular/a.js:8:7)
    at Object.<anonymous> (.../test-circular/main.js:8:3)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)