It is never too late to invest in mutual funds for retirement. As such, if you plan to invest in some of the best funds, the Zacks Mutual Fund Rank can provide you with valuable guidance.

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.

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

Goldman Sachs Small Cap Equity Insights I (GCSIX Quick QuoteGCSIX - Free Report) : 0.84% expense ratio and 0.8% management fee. GCSIX is a Small Cap Blend mutual fund, allowing investors a way to diversify their funds among various types of small-cap stocks. GCSIX has achieved five-year annual returns of an astounding 10.21%.

Putnam Large Cap Value A (PEYAX). Expense ratio: 0.85%. Management fee: 0.45%. PEYAX 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. This fund has managed to produce a robust 15.15% over the last five years.

T. Rowe Price Science & Technology Adviser (PASTX): 1.06% expense ratio and 0.63% management fee. PASTX is part of the Sector - Tech mutual fund category that invests in technology and lets investors own a stake in a notoriously volatile sector, but with a much more diversified approach. The fund is mainly invested in equities, has a long reputation of salutary performance, and has yearly returns of 11.78% 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.