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.

Dreyfus Appreciation Fund Y (DGYGX Quick QuoteDGYGX - Free Report) has a 0.59% expense ratio and 0.55% management fee. DGYGX 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 yearly returns of 12.36% over the last five years, this fund clearly wins.

Fidelity Contrafund K (FCNKX Quick QuoteFCNKX - Free Report) is a stand out amongst its peers. FCNKX 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. With five-year annualized performance of 10.48%, expense ratio of 0.47% and management fee of 0.43%, this diversified fund is an attractive buy with a strong history of performance.

Neuberger Berman Guardian Trust (NBGTX Quick QuoteNBGTX - Free Report) : 1.05% expense ratio and 0.88% management fee. NBGTX 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. With a five-year annual return of 13.24%, 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.