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.

The easiest way to judge a mutual fund's quality over time is by analyzing its performance, diversification, and fees. Using the Zacks Mutual Fund Rank of over 19,000 mutual funds, we've identified three outstanding mutual funds that are ideally suited to help long-term investors pursue and achieve their retirement investing goals.

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

If you are looking to diversify your portfolio, consider

Columbia Small Cap Value I Class Z

(CSCZX Quick QuoteCSCZX - Free Report) . CSCZX is a Small Cap Value mutual fund option, which typically invest in companies with market caps under $2 billion. This fund is a winner, boasting an expense ratio of 1%, management fee of 0.81%, and a five-year annualized return track record of 13.86%.

Goldman Sachs US Equity Dividend & Premier A

(GSPAX Quick QuoteGSPAX - Free Report) : 1.02% expense ratio and 0.7% management fee. GSPAX is a part of the Large Cap Value category, and invests in equities with a market capitalization of $10 billion or more, but whose share prices do not reflect their intrinsic value. With yearly returns of 12.64% over the last five years, GSPAX is an effectively diversified fund with a long reputation of solidly positive performance.

Oppenheimer Discovery R

(ODINX Quick QuoteODINX - Free Report) : 1.32% expense ratio and 0.6% management fee. ODINX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets. With a five-year annual return of 10.84%, this fund is a well-diversified fund with a long track record of success.

We hope that your investment advisor (if you use one) has you invested in one or all of the top-ranked mutual funds we've reviewed. But if that isn't the case, it might be time to have a conversation or reconsider this vitally important relationship.