how do I make a gui element appear in front of an object

You could find the screen coordinates of a 3D world point with Camera.main.WorldToScreenPoint - but be aware that the Y coordinate runs upside down in the GUI system, thus you must invert it.
That's a simple script that shows the object name at offset world units above (script attached to the object):

var width: float = 100; // label width in pixels var height: float = 36; // label height in pixels var offset: float = 2; // offset above object in world units

function OnGUI(){ // calculate the world position for the label: var pos3d = transform.position + Vector3.up * offset; // convert it to screen space: var pos = Camera.main.WorldToScreenPoint(pos3d); // flip the Y coordinate vertically to match GUI space: pos.y = Screen.height - pos.y; // create a rect above pos: var r = Rect(pos.x-width/2, pos.y-height, width, height); // draw it: GUI.Label(r, transform.name); }