From my understanding, if you want to do some macro photography it is better to have a lens that can focus when it is really close to the subject. Sometimes people buy extension tubes to help them achieve this.
My question is: how do I tell before buying a lens how closely it can focus. This doesn't seem to be one of the standard properties listed in the lens name except for maybe when a lens says "macro".
Minimum focusing distance is useful to know, but it is only indirectly related to how much the lens will magnify an image. More to the point is the maximum magnification. This figure is often available (see here for an example) and is typically reported in two ways: in a form like "0.2x", which means an object can be reproduced at 0.2 times life size on the sensor, or "1:5", which means the same thing expressed in reciprocal form. A true macro lens has a maximum magnification of at least 1x (or 1:1). Many good general-purpose lenses have max magnifications around 0.15x to 0.5x.
Sometimes you have to hunt for this information. With Canon lenses, for instance, the max. magnification is usually found at the end of the user manual (available online in pdf format).
A dedicated macro lens will always be a prime lens, at least from Canon/Nikon, they will allow you to get really close. If you have a zoom lens that says Macro, it's only Macro to maybe a foot or two away, which isn't real macro. Most lenses have the minimum focal distance included somewhere on the lens, so keep an eye out for it.