On the large scale, you have something like the Effigy Tumuli by Michael Heizer. The pond skater is perhaps the easiest thing to see in Google Maps. Great big pieces of art made out of the landscape.
You can't get much more massive as a work of art than an extinct volcano. The Roden Crater is a work of art in progress. It has been in progress since the later 1970s. It will allegedly be completed in 2011. It is not yet open to the public, but some people have been lucky enough to see inside this huge piece of land art.
Very few of us happen to own an extinct volcano. So, some more realistic examples of land art might give us ideas of how it can be adapted to a (slightly) smaller stage. Charles Jenks has produced a host of landscapes based on forming the land into art. His own Garden of Cosmic Speculation is something I would like to see, but it is rarely open, and so I will have to make do with photographs, and this review on ThinkinGardens.
On a smaller scale again, Tony Smith's Quilted Velvet garden at Tatton Park gives an idea of what can be done in a garden. Land-forming but in a more realistic way.
It might make mowing the lawn a little difficult, but it adds shape to the garden and would look fantastic with the covering of snow we have at the moment.
Another form of land art is that practiced by the likes of Andy Goldsworthy. These land artworks can be permanent or ephemeral, but are born of their environment and enhance that environment.
Another brilliant example of a land artist I came across on the internet last night is Richard Shilling. He has recently been busy in the snow. His works filled me with so much enthusiasm that I thought I would go out into the garden to make my own ephemeral art in the snow today, but I discovered that there really is such a thing as the wrong sort of snow. It wouldn't hold together at all - I couldn't even make a snowball! Secretly, I am rather glad, as I don't think my efforts and imagination would ever compare with his.
However, I'm up for a challenge and in 2010 I think I will have a go at creating some land art. SomeBeans need not worry - I won't be hiring a digger to re-contour the garden, but one or two attempts at ephemeral art may be forthcoming. Just wish I had the right sort of snow.