At this point, there are about 125 known planets orbiting other stars than the sun. This number grows fairly quickly, but is based on indirect observations of star "wobble".

The planets are detected by their gravitation effects on the star that they orbit. Recently, there has been direct observation of a planet which is known to be too light fusion to take place. It is still large (a few times the size of Jupiter), but is visible in infrared.

Very recently, a very large(larger than Pluto) Kupier Belt object was discovered. Many people think that all of the Kupier Belt objects should not be classified as planets, but if Pluto is a planet, then this new object is likely one as well. You can get the low down at: Caltech here.

Aside from the 185 planets found turning around stars other than our Sun, recently a new planet in our own solar system was discovered beyond the orbit of Pluto. This new planet (temporarily named Xena) looks very much like Pluto, and very much like other Kuiper Belt objects which look more like asteroids (big rocks in space) rather than real planets.

Before Xena, the last planet discovered in our solar system was Pluto, found by Clyde Tombaugh, through a telescope in Arizona, in 1930.