It's the basic question when investing in a stock: is it on the way up or will it go down? To answer this question,  Wall Street has developed numerous ways of attempting to predict what will happen, estimating various attributes tied to stock performance in order to determine what the future holds for a company's valuation. After dissecting the data, analysts following a particular stock produce a price target of where they believe the  stock is headed. Out of the entire S&P 500, which stocks are analysts expecting to have the biggest price drops?  Here's the top 20, according to ThomsonReuters (as of market close on 10/16/09). Click ahead to find out!