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.