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 investors' portfolios.

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

Columbia Small Cap Value I Class R (CSVRX Quick QuoteCSVRX - Free Report) : 1.47% expense ratio and 0.81% management fee. CSVRX is a Small Cap Value fund, and these funds are known for investing in companies with market caps under $2 billion. With annual returns of 15.39% over the last five years, this fund is a winner.

Nuveen LargeCap Growth R6 (TILGX). Expense ratio: 0.41%. Management fee: 0.39%. TILGX is a part of the Large Cap Growth mutual fund category, which invest in many large U.S. companies that are expected to grow much faster compared to other large-cap stocks. This fund has managed to produce a robust 14.99% over the last five years.

American Funds Income Fund of America R6 (RIDGX): 0.25% expense ratio and 0.23% management fee. RIDGX 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. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 10.76% over the last five years.

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.