PrimitiveType.Sphere  

// Creates a sphere primitive
function Start () {
var sphere : GameObject = GameObject.CreatePrimitive(PrimitiveType.Sphere);
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
void Start() {
GameObject sphere = GameObject.CreatePrimitive(PrimitiveType.Sphere);
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

def Start():
sphere as GameObject = GameObject.CreatePrimitive(PrimitiveType.Sphere)