A simple wrapper class for Gizmos which quickens up the gizmos drawing process. Also allows you to draw things like circles and AABB's quickly.

Gizmo draw

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

namespace De.Bug
{
	public class DebugDrawVO : ScriptableObject {
		
		public List<Vector3> Points;
		public Color Color;
		public bool AutoDelete;
	}

	public class Draw : MonoBehaviour {

		public List<DebugDrawVO> Vos = new List<DebugDrawVO>();
		private List<DebugDrawVO> _removing = new List<DebugDrawVO>();

		private static Draw _instance;
		public static Draw Instance
		{
			get{
				if(_instance == null)
				{
					_instance = FindObjectOfType<Draw>();
				}
				if(_instance == null)
				{
					GameObject go = new GameObject();
					_instance = go.AddComponent<Draw>();
					go.name = "Debug Draw";
				}
				return _instance;
			}
		}

		public static void Line(Color color, params Vector3[] point)
		{
			DebugDrawVO vo = ScriptableObject.CreateInstance<DebugDrawVO>();
			List<Vector3> p = new List<Vector3>();
			int i = 0, l = point.Length;
			for(;i<l;++i)
			{
				p.Add(point[i]);
			}
			vo.Points = p;
			vo.Color = color;
			vo.AutoDelete = true;
			Draw.Instance.Vos.Add(vo);
		}

		public static void Line(Color color, List<Vector3> points, bool autoDelete = true)
		{
			DebugDrawVO vo = ScriptableObject.CreateInstance<DebugDrawVO>();
			vo.Points = points;
			vo.Color = color;
			vo.AutoDelete = autoDelete;
			Draw.Instance.Vos.Add(vo);
		}

		public static void AABB(Color color, GameObject gameObject, bool autoDelete = true)
		{
			if(gameObject.transform.renderer == null)
			{
				return;
			}

			DebugDrawVO vo = ScriptableObject.CreateInstance<DebugDrawVO>();
			Vector3 min = gameObject.transform.renderer.bounds.min;
			Vector3 max = gameObject.transform.renderer.bounds.max;

			List<Vector3> p = new List<Vector3>();
			p.Add(new Vector3(min.x,min.y,min.z));
			p.Add(new Vector3(min.x,min.y,max.z));

			p.Add(new Vector3(min.x,min.y,max.z));
			p.Add(new Vector3(max.x,min.y,max.z));

			p.Add(new Vector3(max.x,min.y,max.z));
			p.Add(new Vector3(max.x,min.y,min.z));

			p.Add(new Vector3(max.x,min.y,min.z));
			p.Add(new Vector3(min.x,min.y,min.z));

			p.Add(new Vector3(min.x,max.y,min.z));
			p.Add(new Vector3(min.x,max.y,max.z));
			
			p.Add(new Vector3(min.x,max.y,max.z));
			p.Add(new Vector3(max.x,max.y,max.z));
			
			p.Add(new Vector3(max.x,max.y,max.z));
			p.Add(new Vector3(max.x,max.y,min.z));
			
			p.Add(new Vector3(max.x,max.y,min.z));
			p.Add(new Vector3(min.x,max.y,min.z));

			p.Add(new Vector3(max.x,max.y,min.z));
			p.Add(new Vector3(max.x,min.y,min.z));

			p.Add(new Vector3(max.x,min.y,max.z));
			p.Add(new Vector3(max.x,max.y,max.z));

			p.Add(new Vector3(min.x,max.y,max.z));
			p.Add(new Vector3(min.x,min.y,max.z));

			vo.Points = p;
			vo.Color = color;
			vo.AutoDelete = autoDelete;
			Draw.Instance.Vos.Add(vo);
		}

		public static void Circle(Color color, Vector3 point, float radius, Quaternion rotation, bool autoDelete = true)
		{
			Circle(color,point,radius,rotation.eulerAngles,autoDelete);
		}

		public static void Circle(Color color, Vector3 point, float radius, Vector3 rotation, bool autoDelete = true)
		{
			int segments = (int)(radius*50);
			float angle = (360f) / (float)segments;
			float a = angle;
			List<Vector3> points = new List<Vector3>();
			
			int i = 0, l = segments+1;

			Matrix4x4 m = Matrix4x4.TRS(Vector3.zero,Quaternion.Euler(rotation),Vector3.one);
			
			for (; i<l; ++i)
			{
				Vector3 pos = Vector3.zero;
				float ca = radius * Mathf.Sin(angle * Mathf.Deg2Rad);
				float cb = radius * Mathf.Cos(angle * Mathf.Deg2Rad);
				pos = new Vector3(ca,cb,0);
				pos = m.MultiplyPoint3x4(pos);
				pos.x += point.x;
				pos.y += point.y;
				pos.z += point.z;

				points.Add(pos);
				
				angle += a;
			}

			DebugDrawVO vo = ScriptableObject.CreateInstance<DebugDrawVO>();
			vo.Points = points;
			vo.Color = color;
			vo.AutoDelete = autoDelete;
			Draw.Instance.Vos.Add(vo);
		}

		public static void Sphere(Color color, Vector3 point, float radius, bool autoDelete = true)
		{
			int segments = (int)(radius*50);
			float angle = (360f) / (float)segments;
			float a = angle;
			List<Vector3> pointsa = new List<Vector3>();
			List<Vector3> pointsb = new List<Vector3>();
			List<Vector3> pointsc = new List<Vector3>();
			
			int i = 0, l = (segments*3)+3;
			for (; i<l; ++i)
			{
				Vector3 pos = Vector3.zero;

				float ca = radius * Mathf.Sin(angle * Mathf.Deg2Rad);
				float cb = radius * Mathf.Cos(angle * Mathf.Deg2Rad);

				if(i <= segments)
				{
					pos = new Vector3(point.x + ca,point.y + cb, point.z);
					pointsa.Add(pos);
				}
				else if (i <= (segments * 2)+1)
				{
					pos = new Vector3(point.x + ca,point.y, point.z + cb);
					pointsb.Add(pos);
				}
				else
				{
					pos = new Vector3(point.x,point.y + ca, point.z + cb);
					pointsc.Add(pos);
				}
				

				angle += a;
			}
			DebugDrawVO vo = ScriptableObject.CreateInstance<DebugDrawVO>();
			vo.Points = pointsa;
			vo.Color = color;
			vo.AutoDelete = autoDelete;
			Draw.Instance.Vos.Add(vo);

			vo = ScriptableObject.CreateInstance<DebugDrawVO>();
			vo.Points = pointsb;
			vo.Color = color;
			vo.AutoDelete = autoDelete;
			Draw.Instance.Vos.Add(vo);

			vo = ScriptableObject.CreateInstance<DebugDrawVO>();
			vo.Points = pointsc;
			vo.Color = color;
			vo.AutoDelete = autoDelete;
			Draw.Instance.Vos.Add(vo);
		}

		private void RemoveOldData(List<DebugDrawVO> vosToRemove)
		{
			int i = 0, l = vosToRemove.Count;
			for(;i<l;++i)
			{
				int index = Vos.IndexOf(vosToRemove[i]);
				Destroy(Vos[index]);
				Vos.RemoveAt(index);
			}
		}

		//Do the actual debug stuff in gizmos
		void OnDrawGizmos()
		{
			if(!Debug.isDebugBuild)
			{
				return;
			}

			_removing = new List<DebugDrawVO>();

			int i = 0, l = Vos.Count;
			for(;i<l;++i)
			{
				DebugDrawVO vo = Vos[i];
				if(vo.Points != null)
				{
					Gizmos.color = vo.Color;
					int j = 1, k = vo.Points.Count;
					for(;j<k;++j)
					{
						Gizmos.DrawLine(vo.Points[j-1],vo.Points[j]);
					}
				}
				if(vo.AutoDelete)
				{
					_removing.Add(vo);
				}
			}
		}

		//need to remove the data outside of OnDrawGizmos so they draw in the game view
		void LateUpdate()
		{
			RemoveOldData(_removing);
		}
	}
}