There have actually been a few discoveries in recent years. This one, 2003 UB313, is the biggest at around 3000km across (it was discovered in 2003, but has now been officially confirmed). It is in all probability larger than Pluto (it's a bit fainter, but 3 times further away). The relative distance is shown by this diagram:
There have also been 2003 EL61, which is smaller than Pluto, and 2001 KX76 (which is around 1270km across), quite near Pluto itself.
So do we have 9, 10, 11, 12 planets? Important people are in the process of deciding the issue; do we classify these new findings as "worlds" and add them to our list of planets, or do we de-classify Pluto? That's the source of the contention; if we've classified Pluto as a planet, then so should these. If we don't, then Pluto should no longer officially been seen as a planet.