Jon Markman, the author and MarketWatch columnist, says the S&P 500 Index has plenty of room for growth and could go as high as 3,000 by 2020.

The market still has a lot of potential for investors who are patient because of low interest rates and interest in investing in corporate bonds, Markman told Yahoo Finance Tech Ticker. He says investors should go long.

“It’s still the right thing to be long. This is the most morose bull market in history,” he said.

The S&P 500 recently traded at about 1,166.

“If the public doesn't get on board with this bull market, the companies are going to do it themselves both by buying other companies, and bidding up the market that way, and buying back their own stock.”

Hesitant investors can still take advantage of potential upside in the market. The S&P 500 rose fivefold in the early 1990s after government bailouts, Markman said.

“Something along those lines could happen again,” he aid.

He recommends investing in regional banks, insurance firms and companies such as Apple and Boeing.

The European debt crisis could affect stocks in the short term, Bloomberg reported.

“I think we’ll see strong performances from corporate America, but we’re going to have this dynamic in the background with respect to the well being of these countries whose sovereign debts are now being marked down. The fear is that this is going to set off a domino effect,” said Matthew Kaufler, a portfolio manager at Federated Clover Investment Advisors in Rochester, New York, which manages $3 billion.

The ramifications of weak sovereign debt could affect the economy for awhile.

“Sovereign debt issues is a serious situation, and it’s going to be with us for years. This is a story about debt gone bad, which is the story of the last five years,” said Ralph Shive, manager of the $1.7 billion Wasatch-1st Source Income Equity Fund.