There is a simple predictive model that is built on an assumption that the stock market has a semi-cyclical nature. Many technical analysts use cycle analysis in their comprehensive research. The cycles may not be stable all the time but the probability of repeating patterns can be big enough to get a consistent trading profit.
Cycle analysis can be made using charts. However, the distinctive cycles in pattern can be masked by more powerful factors (fundamental data, bad/good news, global events, etc.) that over-drive the market time-from-time. Therefore, a special software can be very useful for extracting hidden cycles.
The chart below shows S&P-500 index forecast for April-May and summer months of 2012. The calculation has been performed using Stock Market Predictor SMAP-3. According to this forecast the stock market might continue its uptrend until the end of May, then have some correction in June and top in July.