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, perhaps no stock market trend is more popular than value investing, which is a strategy that has proven to be successful in all sorts of market environments. Value investors rely on traditional forms of analysis on key valuation metrics to find stocks that they believe are undervalued, leaving room for profits.Luckily, Zacks has developed its own Style Scores system in an effort to find stocks with specific traits. Value investors will be interested in the system's "Value" category. Stocks with both "A" grades in the Value category and high Zacks Ranks are among the strongest value stocks on the market right now.One stock to keep an eye on is Navios Maritime Partners LP (NMM). NMM is currently holding a Zacks Rank of #1 (Strong Buy) and a Value grade of A. The stock has a Forward P/E ratio of 2.09. This compares to its industry's average Forward P/E of 5.01. Over the past year, NMM's Forward P/E has been as high as 5.06 and as low as 1.70, with a median of 2.67.Investors should also recognize that NMM has a P/B ratio of 0.51. 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 0.99. Over the past year, NMM's P/B has been as high as 0.69 and as low as 0.09, with a median of 0.31.Value investors also frequently use the P/S ratio. This metric is found by dividing a stock's price with the company's revenue. Some people prefer this metric because sales are harder to manipulate on an income statement. This means it could be a truer performance indicator. NMM has a P/S ratio of 1.55. This compares to its industry's average P/S of 1.7.Finally, we should also recognize that NMM has a P/CF ratio of 2.26. This figure highlights a company's operating cash flow and can be used to find firms that are undervalued when considering their impressive cash outlook. This company's current P/CF looks solid when compared to its industry's average P/CF of 6.25. Within the past 12 months, NMM's P/CF has been as high as 352.53 and as low as -91.21, with a median of 2.11.Value investors will likely look at more than just these metrics, but the above data helps show that Navios Maritime Partners LP is likely undervalued currently. And when considering the strength of its earnings outlook, NMM sticks out at as one of the market's strongest value stocks. Breakout Biotech Stocks with Triple-Digit Profit Potential The biotech sector is projected to surge beyond $2.4 trillion by 2028 as scientists develop treatments for thousands of diseases. They’re also finding ways to edit the human genome to literally erase our vulnerability to these diseases. Zacks has just released Century of Biology: 7 Biotech Stocks to Buy Right Now to help investors profit from 7 stocks poised for outperformance. Recommendations from previous editions of this report have produced gains of +205%, +258% and +477%. The stocks in this report could perform even better.See these 7 breakthrough stocks 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 Navios Maritime Partners LP (NMM): Free Stock Analysis Report To read this article on Zacks.com click here.