I've seen many round tower techniques that use tire treads or hinge bricks. However, many of these pieces are hard to amass in quantities. I therefore offer in partial solution two techniques using nothing more than plates, bricks, and Travis bricks.
This one was inspired by a technique I saw on Brickshelf that got a similar effect by using headlight bricks.
This one was inspired in part by DNL's own forays into round towers.