It is never too late to invest in mutual funds for retirement. As such, if you plan to invest in some of the best funds, the Zacks Mutual Fund Rank can provide you with valuable guidance.

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.

AQR Large Cap Momentum Style N (AMONX Quick QuoteAMONX - Free Report) : 0.65% expense ratio and 0.25% management fee. AMONX 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. AMONX has achieved five-year annual returns of an astounding 10.24%.

Dreyfus Strategic Value Y (DRGYX Quick QuoteDRGYX - Free Report) : 0.64% expense ratio and 0.6% management fee. DRGYX 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. DRGYX, with annual returns of 11.31% over the last five years, is a well-diversified fund with a long track record of success.

Fidelity Advisor Mega Cap Stock Z (FZALX Quick QuoteFZALX - Free Report) : 0.51% expense ratio and 0.42% management fee. FZALX is a Large Cap Blend fund, targeting companies with market caps of over $10 billion. These funds offer investors a stability, and are perfect for people with a "buy and hold" mindset. With a five-year annual return of 12.77%, this fund is a well-diversified fund with a long track record of success.

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.