AddForce LimitSpeed with acceleration and deceleration?

First, get the rigidbody's velocity (http://docs.unity3d.com/ScriptReference/Rigidbody-velocity.html). Check to see if the sqrMagnitude of that velocity is greater than your max speed (http://docs.unity3d.com/ScriptReference/Vector3-sqrMagnitude.html), If the velocity is too high then you have some options to slow it down.

Option 1 - increase the drag until the velocity is below your set mark. This will act like the brakes on a car. Add more and more drag to stop faster.

Option 2 - Get the inverse of the vector using gameObject.transform.InverseTransformDirection(velocity) (http://docs.unity3d.com/ScriptReference/Transform.InverseTransformDirection.html). Then use that inverted velocity vector to add force to your object until it is slowed.

Option 3 - Calculate the velocity using Vector3.Lerp (http://docs.unity3d.com/ScriptReference/Vector3.Lerp.html). This one's a bit more complicated since you'll need to take the current velocity, normalize it, and then multiply it by the desired magnitude velocity. That's the endpoint of the lerp. This will, however give you control over the amount of time the deceleration takes place.

Another option would be to try to stop at a certain position. This one's a bit complicated and would require lerping the position over the proper deceleration time. I'm not sure if you can do this and make it look very realistic, so I'd say use one of the other methods and if you really need to stop at a specific point it might be better to not use Unity's physics engine :P

As for providing you with examples, they're mostly in the manual. You just need to write the code based on the above principles and learn. Unity's manual has a lot of great info and you might find the Vector Cookbook section of some use (http://docs.unity3d.com/Manual/VectorCookbook.html).