Creating a plane, adding a texture on both sides and rotating the object on its side

For an example of a repeating texture, check out the source of the example at:

http://stemkoski.github.com/Three.js/Texture-Repeat.html

I recommend the following changes to your code:

var texture, material, plane;

texture = THREE.ImageUtils.loadTexture( "../img/texture.jpg" );

// assuming you want the texture to repeat in both directions:
texture.wrapS = THREE.RepeatWrapping; 
texture.wrapT = THREE.RepeatWrapping;

// how many times to repeat in each direction; the default is (1,1),
//   which is probably why your example wasn't working
texture.repeat.set( 4, 4 ); 

material = new THREE.MeshLambertMaterial({ map : texture });
plane = new THREE.Mesh(new THREE.PlaneGeometry(400, 3500), material);
plane.material.side = THREE.DoubleSide;
plane.position.x = 100;

// rotation.z is rotation around the z-axis, measured in radians (rather than degrees)
// Math.PI = 180 degrees, Math.PI / 2 = 90 degrees, etc.
plane.rotation.z = Math.PI / 2;

scene.add(plane);

Was searching for solution without duplicating all my geometry.

Here you go ladies and gentlemen...

var materials = [new THREE.MeshBasicMaterial({map: texture, side: THREE.FrontSide}),
                 new THREE.MeshBasicMaterial({map: textureBack, side: THREE.BackSide})];

var geometry = new THREE.PlaneGeometry(width, height);

for (var i = 0, len = geometry.faces.length; i < len; i++) {
    var face = geometry.faces[i].clone();
    face.materialIndex = 1;
    geometry.faces.push(face);
    geometry.faceVertexUvs[0].push(geometry.faceVertexUvs[0][i].slice(0));
}

scene.add(new THREE.Mesh(geometry, new THREE.MeshFaceMaterial(materials)));

BOOM a Two Faced Plane for ya, the loop will also work with geometries with more faces, replicating each face and applying the BackSide texture to it.

Enjoy!

I was looking for the same thing and you've just used the property THREE.DoubleSide on the wrong object. You should use it on the material rather than on the mesh itself:

material.side = THREE.DoubleSide;

...nothing more !