While the proven Zacks Rank places an emphasis on earnings estimates and estimate revisions to find strong stocks, we also know that investors tend to develop their own individual strategies. With this in mind, we are always looking at value, growth, and momentum trends to discover great companies.Of these, value investing is easily one of the most popular ways to find great stocks in any market environment. Value investors use a variety of methods, including tried-and-true valuation metrics, to find these stocks.Zacks has developed the innovative Style Scores system to highlight stocks with specific traits. For example, value investors will be interested in stocks with great grades in the "Value" category. When paired with a high Zacks Rank, "A" grades in the Value category are among the strongest value stocks on the market today.One stock to keep an eye on is Navios Maritime Partners LP (NMM). NMM is currently sporting a Zacks Rank of #2 (Buy) and an A for Value. The stock is trading with P/E ratio of 2.26 right now. For comparison, its industry sports an average P/E of 5.88. Over the past 52 weeks, NMM's Forward P/E has been as high as 5.06 and as low as 1.61, with a median of 2.75.Investors should also recognize that NMM has a P/B ratio of 0.47. The P/B ratio pits a stock's market value against its book value, which is defined as total assets minus total liabilities. This stock's P/B looks solid versus its industry's average P/B of 1.02. Over the past 12 months, NMM's P/B has been as high as 0.69 and as low as 0.09, with a median of 0.22.Finally, our model also underscores that NMM has a P/CF ratio of 1.85. This data point considers a firm's operating cash flow and is frequently used to find companies that are undervalued when considering their solid cash outlook. This stock's P/CF looks attractive against its industry's average P/CF of 5.91. Over the past year, NMM's P/CF has been as high as 352.53 and as low as -127.95, with a median of 1.99.These figures are just a handful of the metrics value investors tend to look at, but they help show that Navios Maritime Partners LP is likely being undervalued right now. Considering this, as well as the strength of its earnings outlook, NMM feels like a great value stock at the moment. More Stock News: This Is Bigger than the iPhone! It could become the mother of all technological revolutions. Apple sold a mere 1 billion iPhones in 10 years but a new breakthrough is expected to generate more than 77 billion devices by 2025, creating a $1.3 trillion market. Zacks has just released a Special Report that spotlights this fast-emerging phenomenon and 4 tickers for taking advantage of it. If you don't buy now, you may kick yourself in 2022.Click here for the 4 trades >>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 Navios Maritime Partners LP (NMM): Free Stock Analysis Report To read this article on Zacks.com click here.