The funds in our "Magnificent Retirement Mutual Funds" list are some of the top-performing, best managed funds available. If you're already invested in them, congratulations! If you're not, don't worry - it's never too late to start getting the advantages of these outstanding funds for your retirement.

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 our Zacks Rank, we've found three mutual funds that would be great additions to any long-term retirement investors' portfolios.

Let's break down some of the mutual funds with the highest Zacks Rank and the lowest fees.

Principal Blue Chip Fund A (PBLAX Quick QuotePBLAX - Free Report) : 0.93% expense ratio and 0.61% management fee. PBLAX 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 annual returns of 15.88% over the last five years, this fund is a winner.

MassMutual Select Mid Cap Growth Service Class (MEFYX Quick QuoteMEFYX - Free Report) : 0.91% expense ratio and 0.68% management fee. MEFYX is a Mid Cap Growth mutual fund. These funds aim to target companies with a market capitalization between $2 billion and $10 billion that are also expected to exhibit more extensive growth opportunities for investors than their peers. With yearly returns of 10.76% over the last five years, MEFYX is an effectively diversified fund with a long reputation of solidly positive performance.

Putnam Small Cap Growth R (PSGRX Quick QuotePSGRX - Free Report) . Expense ratio: 0.74%. Management fee: 0.65%. Five year annual return: 10.9%. PSGRX is a Small Cap Growth mutual fund and tends to feature small companies in up-and-coming industries and markets.

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.

Do You Know the Top 9 Retirement Investing Mistakes?

Investing in underperforming mutual funds is just one of the key errors that can derail your retirement plans.

To learn more, read our just-released report: 9 Retirement Mistakes You Need to Avoid.