The first exoplanets discovered by astronomers have, not surprisingly, been gas giants like our own neighbor Jupiter. As techniques and instruments have been refined (most notably with the addition of NASA's orbiting Kepler observatory), a class of smaller exoplanets, nicknamed "Super-Earths," has been discovered. These are still several times larger than our own planet, but astronomers are confident we'll soon be identifying Earth-sized worlds. A new generation of instruments (which NASA planned but abandoned in its Terrestrial Planet Finder program) will be needed to nail down the possibilities of life. My prediction: eventually, we'll find it.
"It is inconceivable that the whole universe was merely created for us who live in this third-rate planet of a third-rate sun." - Alfred, Lord Tennyson