ContactPoint.normal  

// Print how many points are colliding this transform 
// And print the first point normal that is colliding.
function OnCollisionEnter(other : Collision) {
     print("Points colliding: " + other.contacts.Length);
    print("First normal of the point that collide: " + other.contacts[0].normal);
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void OnCollisionEnter(Collision other) {
        print("Points colliding: " + other.contacts.Length);
        print("First normal of the point that collide: " + other.contacts[0].normal);
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def OnCollisionEnter(other as Collision):
        print(('Points colliding: ' + other.contacts.Length))
        print(('First normal of the point that collide: ' + other.contacts[0].normal))