The proven Zacks Rank system focuses on earnings estimates and estimate revisions to find winning stocks. Nevertheless, we know that our readers all have their own perspectives, so we are always looking at the latest trends in value, growth, and momentum to find strong picks.Of these, value investing is easily one of the most popular ways to find great stocks in any market environment. Value investors use fundamental analysis and traditional valuation metrics to find stocks that they believe are being undervalued by the market at large.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.Sallie Mae (SLM) is a stock many investors are watching right now. SLM is currently sporting a Zacks Rank of #2 (Buy), as well as an A grade for Value. The stock is trading with a P/E ratio of 3.52, which compares to its industry's average of 8.24. Over the past 52 weeks, SLM's Forward P/E has been as high as 9.03 and as low as 3.20, with a median of 6.72.Investors should also note that SLM holds a PEG ratio of 0.32. 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. SLM's PEG compares to its industry's average PEG of 0.72. SLM's PEG has been as high as 0.70 and as low as 0.29, with a median of 0.47, all within the past year.Finally, our model also underscores that SLM has a P/CF ratio of 4.56. 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. SLM's current P/CF looks attractive when compared to its industry's average P/CF of 5.05. Over the past 52 weeks, SLM's P/CF has been as high as 8.33 and as low as 4.14, with a median of 6.46.These figures are just a handful of the metrics value investors tend to look at, but they help show that Sallie Mae is likely being undervalued right now. Considering this, as well as the strength of its earnings outlook, SLM 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 SLM Corporation (SLM): Free Stock Analysis Report To read this article on Zacks.com click here.