When it comes to close-up photography you have several options; this article discusses close up lenses.  For extension tubes please see here.

Although they are actually lenses they are commonly called close-up filters due to the fact they attach to your lens using the front filter thread.  Don't get me wrong, you can't beat a dedicated macro lens such as the Canon 100mm f/2.8 Macro when it comes to getting up close and personal, but close-up lenses can go a long way when first experimenting with close-up photography.

Available in a various diopters such as +1, +2, +4 and +10 they can also be stacked to increase the magnification.  You should be careful when doing this as image quality will suffer as a result of all the extra glass surfaces.  See below for an example of their effect:

As you can see they do very well at filling the entire frame with small objects.  This is actually achieved by reducing the minimum focusing distance of the lens, allowing you to get physically closer and therefore increasing magnification.  They are best used on telephoto lenses as standard lenses have relatively small minimum focusing distances to begin with and the effect is reduced.  For standard lenses I highly recommend using a set of Kenko extension tubes.

Considering that they can be found for under £20 for a 58mm filter size, why not grab a close-up lens for your kit lens and start looking for subjects under your feet?

The shot below was taken with the Canon EF-S 18-55mm f/3.5-5.6 kit lens and +4 diopter close-up lens.