From my own past experiences, bookends are either too bulky or too light to support the weight of the books. Perhaps you haven't got any bookends? Well. Think you really need them? Think again. By using the books themselves, in most situations, you can actually create a nice little arrangement without needing anything else! Exhibit A:
(above) I put my "stylist" hat on and this was the result. See! Not a bookend in sight! Doesn't look too shabby, either.