More than 5000 such planets have been identified, not all of which have been independently confirmed. In the Milky Way galaxy, it is expected that there are many billions of planets (at least one planet, on average, orbiting around each star, resulting in 100400 billion exoplanets, with many more free-floating planetary-mass bodies orbiting the galaxy directly.
The nearest known exoplanet is Alpha Centauri Bb.

Of the 1854 confirmed exoplanets (as of Dec 2014), the Kepler space telesope had found 132 of them in 76 stellar systems, along with a further 3,216 unconfirmed planet candidates, including 54 that may be in the habitable zone. Six candidates in this zone were thought to be smaller than twice the size of Earth. The Kepler mission has detected over 18,000 additional transit events, including 262 that may be habitable planets.

 Almost all of the planets detected so far are within the Milky Way; however, there have been a small number of possible detections of extragalactic planets.

Some known exoplanet systems from Astronomy Magazine, Feb 2015.