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.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.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 company value investors might notice is Donegal Group (DGICA). DGICA is currently sporting a Zacks Rank of #2 (Buy), as well as a Value grade of A. The stock has a Forward P/E ratio of 11.79. This compares to its industry's average Forward P/E of 31.27. Over the past 52 weeks, DGICA's Forward P/E has been as high as 17.63 and as low as 11.08, with a median of 15.16.Another valuation metric that we should highlight is DGICA's P/B ratio of 0.86. 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 1.40. Over the past 12 months, DGICA's P/B has been as high as 0.95 and as low as 0.79, with a median of 0.85.Value investors also use the P/S ratio. The P/S ratio is is calculated as price divided by sales. This is a prefered metric because revenue can't really be manipulated, so sales are often a truer performance indicator. DGICA has a P/S ratio of 0.57. This compares to its industry's average P/S of 1.06.Stewart Information Services (STC) may be another strong Insurance - Property and Casualty stock to add to your shortlist. STC is a # 1 (Strong Buy) stock with a Value grade of A.Furthermore, Stewart Information Services holds a P/B ratio of 1.72 and its industry's price-to-book ratio is 1.40. STC's P/B has been as high as 1.77, as low as 1.22, with a median of 1.45 over the past 12 months.These are just a handful of the figures considered in Donegal Group and Stewart Information Services'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 DGICA and STC is an impressive value stock right now. Zacks’ Top Picks to Cash in on Artificial Intelligence This world-changing technology is projected to generate $100S of billions by 2025. From self-driving cars to consumer data analysis, people are relying on machines more than we ever have before. Now is the time to capitalize on the 4th Industrial Revolution. Zacks’ urgent special report reveals 6 AI picks investors need to know about today.See 6 Artificial Intelligence Stocks With Extreme Upside Potential>>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 Donegal Group, Inc. (DGICA): Free Stock Analysis Report Stewart Information Services Corporation (STC): Free Stock Analysis Report To read this article on Zacks.com click here. Zacks Investment Research