If you're invested in any of the funds in our "Magnificent Retirement Mutual Funds" list, congratulations on owning some of the best managed and top-performing mutual funds. If you are lucky enough to discover our list of Top-Ranked Funds for the first time, it's never too late to start investing with the best, especially when it comes to your retirement.Great performance, diversification, and low fees: it's a pretty simple formula for a great mutual fund. Some are better than others, but utilizing our Zacks Rank, we have identified three mutual funds that would make great additions to long-term investors' portfolios.Let's take a look at some of the highest Zacks Ranked mutual funds with the lowest fees.Putnam Small Cap Growth Y (PSYGX): 0.99% expense ratio and 0.65% management fee. PSYGX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. With annual returns of 11.46% over the last five years, this fund is a winner.Harbor Capital Appreciation Investor (HCAIX): 1.03% expense ratio and 0.6% management fee. HCAIX is a Large Cap Growth option; these mutual funds purchase stakes in numerous large U.S. companies that are expected to develop and grow at a faster rate than other large-cap stocks. HCAIX, with annual returns of 16.19% over the last five years, is a well-diversified fund with a long track record of success.T. Rowe Price Global Technology (PRGTX): 0.88% expense ratio and 0.74% management fee. PRGTX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 21.67% over the last five years.These examples highlight the fact that there are some astonishingly good mutual funds out there. If your advisor has you in the good ones, bravo! If not, you may need to have a talk.Do You Know the Top 9 Retirement Investing Mistakes?Investing in underperforming mutual funds is just one of the key errors that can derail your retirement plans.To learn more, read our just-released report: 9 Retirement Mistakes You Need to Avoid.This report can help you sidestep these costly mistakes and potentially achieve your retirement goals. Get Your FREE Guide Now Get Your Free (HCAIX): Fund Analysis Report Get Your Free (PRGTX): Fund Analysis Report Get Your Free (PSYGX): Fund Analysis Report To read this article on Zacks.com click here. Zacks Investment Research