A planet which is suspected to be the closet resemblance to Earth has been seen, and its a neighbour.
Just 20 light years away (almost in touching distance) around the star Gliese 581 is a planet not much bigger than Earth (1.5x). It orbits much closer to its star than the Earth does to the Sun, and takes only 13 “Earth” days to orbit. However, the star Gliese is much smaller and weaker than the Sun so a planet orbiting that close would actually have temperatures very similair to Earth, in fact within the temperature limit that would allow liquid water to exist on the surface.
All this has been estimated from the slight wobble of the star seen from Earth, which is created when a something large orbits around, although the effect is very small.
This would make an ideal candidate for the upcoming planet hunting space telescopes, designed to image planets around stars – unfortunately, we still have to wait several decades for this to be achieved…
More info here:
http://obswww.unige.ch/Instruments/harps/Welcome.html (The discovers)