We cover this subject in the post Make Love, War, Wine, or Spacecraft?, which links to other posts and threads that cover the subject in more depth.
This particular search we cover in this post does not involve spacecraft. Instead it involves the analysis of light coming to a telescope near you:
Although Captain Kirk and crew could zip over to a planet at warp speed and teleport down to the surface to check if it was inhabited, current-day scientists will generally have to search for life from a distance. New research gives some hope that we could detect a "handedness" beacon from a planet full of microbes.(Space, emphasis added). Other articles linked to above point out that eventually human kind will have to move to another planet because the Sun is going to destroy the planet earth in the distant future.
This handedness, or homochirality, is characteristic of life on Earth. The molecules that make proteins and DNA all have either a left-handed or right-handed orientation. Both orientations are made in equal quantities by non-biological processes, but life prefers to have just one type of hand over the other.
"Homochirality is a fundamental aspect of self-replication," says William Sparks of the Space Telescope Science Institute. "It is a reasonable proposition that life on other planets will exhibit a particular handedness."
So we keep searching in many ways until we find some good leads.
UPDATE: A water detecting technique is being developed in the Kepler mission. Planets with water will be easier to find as it is perfected.