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.

MFS Mass Investors Growth Stock R3 (MIGHX Quick QuoteMIGHX - Free Report) : 0.71% expense ratio and 0.33% management fee. MIGHX 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. MIGHX has achieved five-year annual returns of an astounding 14.34%.

ProFunds Tech UltraSector Investor (TEPIX Quick QuoteTEPIX - Free Report) is a stand out amongst its peers. TEPIX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector with a much more diversified approach. With five-year annualized performance of 22.85%, expense ratio of 1.43% and management fee of 0.75%, this diversified fund is an attractive buy with a strong history of performance.

Hartford Stock HLS IA (HSTAX Quick QuoteHSTAX - Free Report) . Expense ratio: 0.51%. Management fee: 0.48%. Five year annual return: 12.36%. HSTAX 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.