Investing in mutual funds for retirement is never too late. And the Zacks Mutual Fund Rank can be an excellent tool for investors looking to invest in the best funds.

How can you tell a good mutual fund from a bad one? It's pretty basic: if the fund is diversified, has low fees, and shows strong performance, it's a keeper. Of course, there's a wide range, but using the Zacks Mutual Fund Rank, we've found three mutual funds that would be great additions to any long-term retirement investors' portfolios.

Let's take a look at some of our top-ranked mutual funds with the lowest fees.

Franklin Small-Mid Cap Growth R6 (FMGGX Quick QuoteFMGGX - Free Report) : 0.49% expense ratio and 0.46% management fee. FMGGX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. With annual returns of 11.52% over the last five years, this fund is a winner.

John Hancock Disciplined Value R2 (JDVPX Quick QuoteJDVPX - Free Report) : 1.15% expense ratio and 0.61% management fee. JDVPX is a Large Cap Value mutual fund, which invests in stocks with a market cap of $10 billion of more, but whose share prices do not reflect their intrinsic value. JDVPX, with annual returns of 10.15% over the last five years, is a well-diversified fund with a long track record of success.

JPMorgan US Equity Fund R5 (JUSRX Quick QuoteJUSRX - Free Report) is an attractive large-cap allocation. JUSRX is part of the Large Cap Blend section, and these mutual funds most often invest in firms with a market capitalization of $10 billion or more. By investing in bigger companies, these funds offer more stability, and are often well-suited for investors with a "buy and hold" mindset. JUSRX has an expense ratio of 0.54%, management fee of 0.4%, and annual returns of 15.97% over the past 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.