From Unity 4, assuming a default installation directory these templates are found in: C:\Program Files (x86)\Unity\Editor\Data\Resources\ScriptTemplates
In there, you'll find the JavaScript, C# and Boo script templates along with the shader and compute shader templates.
Here's the C# one:
using UnityEngine;
using System.Collections;
public class #SCRIPTNAME# : MonoBehaviour {
// Use this for initialization
void Start () {
}
// Update is called once per frame
void Update () {
}
}