Here at Zacks, we focus on our proven ranking system, which places an emphasis on earnings estimates and estimate revisions, to find winning stocks. But we also understand that investors develop their own strategies, so we are constantly looking at the latest trends in value, growth, and momentum to find strong companies for our readers.Looking at the history of these trends, perhaps none is more beloved than value investing. This strategy simply looks to identify companies that are being undervalued by the broader market. Value investors use a variety of methods, including tried-and-true valuation metrics, to find these stocks.In addition to the Zacks Rank, investors looking for stocks with specific traits can utilize our Style Scores system. Of course, value investors will be most interested in the system's "Value" category. Stocks with "A" grades for Value and high Zacks Ranks are among the best value stocks available at any given moment.Omnicom (OMC) is a stock many investors are watching right now. OMC is currently sporting a Zacks Rank of #2 (Buy), as well as a Value grade of A. The stock is trading with a P/E ratio of 10.21, which compares to its industry's average of 13.19. Over the past year, OMC's Forward P/E has been as high as 13.45 and as low as 7.56, with a median of 12.05.Investors should also note that OMC holds a PEG ratio of 1.46. This popular figure is similar to the widely-used P/E ratio, but the PEG ratio also considers a company's expected EPS growth rate. OMC's PEG compares to its industry's average PEG of 1.66. Within the past year, OMC's PEG has been as high as 2.69 and as low as 1.36, with a median of 2.37.We should also highlight that OMC has a P/B ratio of 3.99. Investors use the P/B ratio to look at a stock's market value versus its book value, which is defined as total assets minus total liabilities. This stock's P/B looks attractive against its industry's average P/B of 11.51. Within the past 52 weeks, OMC's P/B has been as high as 6.03 and as low as 3.10, with a median of 5.02.Finally, investors will want to recognize that OMC has a P/CF ratio of 9.92. This metric focuses on a firm's operating cash flow and is often used to find stocks that are undervalued based on the strength of their cash outlook. This stock's P/CF looks attractive against its industry's average P/CF of 16.10. Over the past year, OMC's P/CF has been as high as 11.66 and as low as 6.81, with a median of 10.72.These are just a handful of the figures considered in Omnicom's great Value grade. Still, they help show that the stock is likely being undervalued at the moment. Add this to the strength of its earnings outlook, and we can clearly see that OMC is an impressive value stock right now.Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Omnicom Group Inc. (OMC): Free Stock Analysis Report To read this article on Zacks.com click here.