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.Considering these trends, value investing is clearly one of the most preferred ways to find strong stocks in any type of market. Value investors use tried-and-true metrics and fundamental analysis to find companies that they believe are undervalued at their current share price levels.On top of the Zacks Rank, investors can also look at our innovative Style Scores system to find stocks with specific traits. For example, value investors will want to focus on the "Value" category. Stocks with high Zacks Ranks and "A" grades for Value will be some of the highest-quality value stocks on the market today.One stock to keep an eye on is Omnicom (OMC). OMC is currently sporting a Zacks Rank of #2 (Buy), as well as an A grade for Value. The stock holds a P/E ratio of 9.75, while its industry has an average P/E of 12.06. OMC's Forward P/E has been as high as 13.45 and as low as 7.56, with a median of 11.16, all within the past year.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 5.99 and as low as 3.10, with a median of 4.13.Finally, investors will want to recognize that OMC has a P/CF ratio of 9.93. This metric takes into account a company's operating cash flow and can be used to find stocks that are undervalued based on their solid 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 10.07.These figures are just a handful of the metrics value investors tend to look at, but they help show that Omnicom is likely being undervalued right now. Considering this, as well as the strength of its earnings outlook, OMC feels like a great value stock at the moment.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.