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.

Great performance, diversification, and low fees: it's a pretty simple formula for a great mutual fund. Some are better than others, but utilizing our Zacks Rank, we have identified three mutual funds that would make great additions to long-term investors' portfolios.

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

Morgan Stanley Multi-Cap Growth Trust IS (MCRTX Quick QuoteMCRTX - Free Report) : 0.76% expense ratio and 0.65% management fee. MCRTX 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. MCRTX has achieved five-year annual returns of an astounding 27.07%.

MassMutual Select Mid Cap Growth I (MEFZX Quick QuoteMEFZX - Free Report) . Expense ratio: 0.71%. Management fee: 0.68%. MEFZX 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. This fund has managed to produce a robust 10.97% over the last five years.

T. Rowe Price Media & Telecomm (PRMTX Quick QuotePRMTX - Free Report) : 0.76% expense ratio and 0.64% management fee. PRMTX is a Sector - Tech mutual fund, allowing investors to own a stake in a notoriously volatile sector 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 19.51% over the last five years.

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.

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.