An easy implementation for a Wireframe render (to use with the specifical shader).

wireframe.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class Wireframe : MonoBehaviour
{
	public Color lineColor;
	public Material lineMaterial;

	private MeshFilter filter;

	void Start()
	{
		filter = GetComponent<MeshFilter>();
	}

	void OnRenderObject()
	{
		if(lineMaterial== null)
		{
			Debug.Log("no line material");
			return;
		}
		lineMaterial.SetPass(0);

		for(int i = 0; i < filter.mesh.triangles.Length; i++)
		{
			if(i%3 == 0)
			{
				if(i != 0)
					GL.End();
				GL.Begin(GL.LINES);
			}
			GL.Color(lineColor);
			GL.Vertex(transform.TransformPoint(filter.mesh.vertices[filter.mesh.triangles[i]]));
		}
		GL.End ();
	}
}

wireframe.shader

Shader "Custom/Wireframe"
{
	SubShader
	{
		Pass
		{
			Blend SrcAlpha OneMinusSrcAlpha
			ZWrite Off
			Cull Off
			Fog { Mode Off }
			BindChannels
			{
				Bind "vertex", vertex
				Bind "color", color
			}
		}
	}
}