According to physicist Mausimi Dikpati, the next sunspot cycle will be 30-50 percent stronger than the current cycle, and it will peak in 2012.

Researchers at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, have used a new model of the sun's interior to refine predictions of future sunspot activity. By using data going back over a century, the scientists were able to determine that the sun's magnetic field has a memory of around 20 years. This model was able to predict the past six cycles with around 97 percent accuracy, and has led to revised predictions about the next cycle, number 24.

Sources: ArtsTechnica + New Scientist