With the tax filing deadline of April 15 a few days away, investors still have some time to make contributions to their individual retirement accounts (IRAs) for the 2018 tax year.IRAs allow investors to buy stocks, bonds, ETFs and mutual funds. ETFs are excellent tools for retirement investors as well since they provide an easy way to build a diversified portfolio at a low cost. Further, income paying ETFs are better placed in an IRA as income is sheltered from taxes.Before investing for retirement, investors need to assess their investing goals, time horizon and risk tolerance. Low-cost, broad, diversified funds are more suitable for retirement investors as core, long-term investments rather than costly, narrow-focused or niche ETFs.Expense ratio of an ETF should be an important consideration in retirement investing, as in the long-term, cheaper funds can significantly outperform their more expensive counterparts.The iShares Core S&P Total U.S. Stock Market ETF (ITOT) is a convenient way to get exposure to the entire US stock universe, ranging from some of the smallest to largest companies at an extremely low cost of just 3 basis points.It holds more than 3,600 stocks in its basket and should be a core holding in any long-term focused portfolio. Apple (AAPL), Microsoft (MSFT) and Amazon (AMZN) are its top holdings.The Schwab U.S. Large-Cap Value ETF (SCHV) provides broad exposure to large-cap U.S. stocks with value style characteristics. It has an expense ratio of just 4 basis points, while the dividend yield is 2.9%.Numerous academic studies have shown that value stocks have delivered higher returns with lower volatility compared with growth stocks over the long term in almost all the markets studied. Thus value stocks and funds should be a part of any ‘core’ portfolio. The Vanguard Real Estate ETF (VNQ), the most popular REIT ETF, has a juicy dividend yield of 3.3%. REITs are generally rate sensitive and are benefitting a lot from the Fed’s dovish stance. Further, REITs have low correlation with stocks and provide some diversification benefits to the portfolio.To learn more about these ETFs, please watch the short video above.Want key ETF info delivered straight to your inbox?Zacks’ free Fund Newsletter will brief you on top news and analysis, as well as top-performing ETFs, each week. Get it free >>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 Apple Inc. (AAPL): Free Stock Analysis Report Microsoft Corporation (MSFT): Free Stock Analysis Report Schwab U.S. Large-Cap Value ETF (SCHV): ETF Research Reports Vanguard Real Estate ETF (VNQ): ETF Research Reports iShares Core S&P Total U.S. Stock Market ETF (ITOT): ETF Research Reports To read this article on Zacks.com click here. Zacks Investment Research 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