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.

Here are the funds that have achieved the Zacks Mutual Fund Rank #1 (Strong Buy) and have low fees.

Amana Growth Investor (AMAGX Quick QuoteAMAGX - Free Report) : 0.9% expense ratio and 0.62% management fee. AMAGX 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. AMAGX has achieved five-year annual returns of an astounding 13.87%.

Neuberger Berman Guardian Institutional (NGDLX Quick QuoteNGDLX - Free Report) is a stand out amongst its peers. NGDLX is a Large Cap Value fund. These funds invest in stocks with a market cap of $10 billion of more, but whose share prices do not reflect their intrinsic value. With five-year annualized performance of 11.08%, expense ratio of 0.68% and management fee of 0.63%, this diversified fund is an attractive buy with a strong history of performance.

T. Rowe Price Dividend Growth Fund (PRDGX Quick QuotePRDGX - Free Report) : 0.64% expense ratio and 0.48% management fee. PRDGX 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 10.51%, 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.