Selection.transforms  

static var transforms : Transform[]

Description

Returns the top level selection, excluding prefabs.

This is the most common selection type when working with scene objects.

// C# example
// Select Objects and make them look to the main Camera by pressing 'l'
using UnityEngine;
using UnityEditor;

public class LookAtMainCamera : ScriptableObject {
    [MenuItem ("Example/Selection looks at Main Camera _l")]
    static void Look() {
        Camera camera = Camera.main;

        if (camera) {
            foreach (Transform transform in Selection.transforms) {
                Undo.RegisterUndo(transform, transform.name + " Looks at Main Camera" );
                transform.LookAt(camera.transform);
            }
        }
    }
    //The menu item will be disabled if nothing, is selected.
    [MenuItem ("Example/Selection looks at Main Camera _l", true)]
    static bool ValidateSelection () {
        return Selection.transforms.Length != 0;
    }
}