ShakeyCamera.cs

using UnityEngine;
using System.Collections;

public class ShakeyCamera : MonoBehaviour {

    public float recoverStrength = 1;
    public AnimationCurve shakeCurve = new AnimationCurve(new Keyframe[]{ new Keyframe(0,0), new Keyframe(1,1)});
    public Transform shakePivot;

    Vector3 startPosition;
    Vector3 offset;
    float velocity;

    void Awake(){
        startPosition = shakePivot.localPosition;
    }

    void FixedUpdate(){
        velocity -= velocity * Time.deltaTime * recoverStrength;

        if(velocity > 0)
            offset = Random.insideUnitSphere * shakeCurve.Evaluate(velocity) * velocity;

        shakePivot.localPosition = startPosition + offset;
    }

    public void Shake(float force){
        velocity += force;
    }

    [ContextMenu("Shake")]
    void ShakeTest(){
        Shake(Random.value * 10);
    }
}