There are two ways to monitor what stocks are being added. When a stock is added to the exchange, its underwriters set the price that the stock will begin trading. Of course, not all of those IPOs will have their prices set. The second way to watch what stocks are being added to the market is to monitor filings. A filing is when a company expresses interest in going public.
Many companies withdraw their IPOs if the market sours on their industry.
Watching which companies are filing by using the above Web sites gives you an early indicator of the types of companies in the IPO pipeline.