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 learn about some of Zacks' highest ranked mutual funds with low fees you may want to consider.

AB Lg Cap Growth A (APGAX Quick QuoteAPGAX - Free Report) : 0.84% expense ratio and 0.48% management fee. APGAX is a Large Cap Growth mutual fund, and these funds invest in many large U.S. firms that are projected to grow at a faster rate than their large-cap peers. With annual returns of 12.81% over the last five years, this fund is a winner.

Black Oak Emerging Technology Fund (BOGSX Quick QuoteBOGSX - Free Report) . Expense ratio: 1.03%. Management fee: 0.74%. With a much more diversified approach, BOGSX--part of the Sector - Tech mutual fund category--gives investors a way to own a stake in the notoriously risky tech sector. This fund has managed to produce a robust 13.87% over the last five years.

State Street Institutional US Equity Investor (SUSIX Quick QuoteSUSIX - Free Report) . Expense ratio: 0.38%. Management fee: 0.37%. Five year annual return: 11.55%. SUSIX 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.

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.