In order to make it walk around you'd need to basically do 3 things:

1) Pick a random direction (check out Random.insideUnitCircle in scripting help is a good start if its only 2D movement you are after)

2) Send out a ray in that direction, starting from the object and see if it hit anything (check out Collider.Raycast or Physics.Raycast)

3) If the ray did not hit anything, or if it hit something but it is within the acceptable distance away from the object then add some Force to it (if using a Rigidbody component) or lerp the objects transform (iTween or something would help here)

After you made that function you would just randomly call, or call it at an interval to have it meander in different directions. (InvokeRepeating)

You can use UnitySteer. See the examples.

A* might be a good place to start looking: http://www.arongranberg.com/unity/a-pathfinding/

RAIN{indie} is a, free, complete solution for adding pathfinding, movement, sensing, and behavior to any Unity project.

To download RAIN{indie}, just click the link and follow the 2 steps. RAIN{indie}: http://rivaltheory.com/downloadindie

We put together a compilation of tutorials and documents from the RAIN{indie} AI community that supplements our own support resources http://bit.ly/W47KSO

FAQs to learn more about the differences between RAIN{one} and RAIN{indie} as well as many other answers. http://support.rivaltheory.com/documentation/faq

Email me jester@rivaltheory.com if you have any questions.

So I have been trying to work out a basic little code to make it wander, (without avoiding collisions yet) but it doesn't seem to be working. This is the code I have worked out so far.

var speed : int= 5;
var wayPoint : Vector2;

function Start()
{
    InvokeRepeating("Wander", 2, 20);
}

function Wander()
{
    var wayPoint : Vector2= Random.insideUnitCircle *47;
    Debug.Log(wayPoint);
}

function Update() 
{
    transform.LookAt(wayPoint);
    rigidbody.AddRelativeForce(Vector3.forward * speed);
}

It moves if I set wayPoint to a position in the inspector but it moves only to the right and up. This is probably because Vector2 uses only the x and y axis. My problem is that I do not know how to make something move 2 dimensionally across the x and z axis. Any ideas? Why do I have to set it(wayPoint) to a position before it will work? I would've posted this is a comment but then I wouldn't have been able to insert my code.