The trailing 12 month Price to Earnings ratio on the S&P 500 has fallen from 18.5 to 16.75 over the last week. This means stocks have become less expensive relative to their earnings (lower priced stocks are more attractive to purchase for value investors).
Stocks are historically considered cheap when their trailing P/E ratio moves under 10 so we would need the S&P 500 to fall about 40% from here for stocks to provide a safe long term entry point. In addition, earnings would need to remain at the level they are today (price is only half the equation). If earnings fell (they are sitting at all time record highs), then stocks would need to fall significantly more than 40% in order to provide a safe, attractive entry point.
Just a quick big picture overview for those hunting for bargains in the United States after the recent decline. Save your time; they don't exist (yet).