Photo by Bryan Rosengrant, Flickr Creative Commons.

Stock markets are off to a historically bad start for the year, and the S&P 500 has officially plunged into correction territory. With weaknesses in the commodity and emerging markets weighing on investors' minds, it's possible that stocks could continue to decline, even from today's depressed prices.

While it's never fun to watch the share prices of companies you own decline so rapidly, it's times like these that are great opportunities for long-term-oriented investors to go bargain-hunting. Following are three stocks that I think are ideal long-term holdings that would be tempting to pick up any time -- but particularly in a market crash when they go on sale.

1. Celgene (CELG)
Biotech blue chip Celgene has been a phenomenal stock to own for years. Thanks to the amazing success of Revlimid, its treatment for multiple myeloma, the company's revenues and profits continue to climb ever higher, and a recently announced deal should ensure that trend continues for years to come.

Late last year, Celgene reached an agreement with Natco Pharma, which was threatening to bring biosimilar copycats of Revlimid to market. The terms of the deal allow Natco Pharma to sell a limited supply of its biosimilar between 2022 and 2025, with no limits on the quantity it can sell thereafter.

The certainty that comes with this deal was a huge win for Celgene's investors. Celgene is heavily dependent on Revlimid's ability to produce billions in revenue, so it's great news that the cash will keep flowing in for years to come. 

Image Source: Celgene.

However, this Revlimid deal is far from the only reason to be bullish on Celegne's prospects. Celgene also sells several other drugs -- namely, Pomalyst, Abraxane, and Otezla -- that should each show strong growth over the coming years and produce billions in revenue for the company. A little bit further down the road, Celgene's $7.2 billion purchase of Receptos should begin to pay dividends. The crown jewel of the Receptos purchase was Ozanimod, a promising immunotherapy. Ozanimod has a good chance of making its way to market, and analysts believe it holds peak sales potential of more than $4 billion annually.

Management projects that by 2020, the company will have product sales exceeding $21 billion, which will allow it to show earnings per share of at least $13.00. If it can get there, the company's current stock price will probably look like a bargain in retrospect, and even more so if the market were to discount shares further from here.

2. Visa (V -4.26%)
Economies worldwide continue to move toward electronic payment processing, which has been a lucrative trend for Visa to ride. Sales at the payment giant have grown by more than 11% annually over the past five years, and a combination of regular share repurchases mixed with its fixed-cost business model has allowed its earnings per share to grow by an even faster 22% over the same time period.

As good as these results have been, there are plenty of reasons to be even more bullish about Visa's near-term future. First, Visa is pushing aggressively to build out its network in China, which is an enormous market that gives the company huge room to expand. Next, its pending acquisition of Visa Europe will add back a major economic center to its empire. The company will also be welcoming Costco as a major new customer to its network later this year.

Add it all up, and Visa is expecting that payment volumes will increase at a faster rate than the 11% it's seen over the past few years. Although profits may temporarily be held back as it ramps up its investments in Europe and China, over the long term those investments look poised to pay off in spades.

3. Priceline Group (BKNG -2.00%)
The recent strengthening of the U.S. dollar has masked the true results of many companies that do a substainial amount of business in foreign markets. One company that's been hit especially hard is Priceline Group, which generates the vast majority of its revenue and profit overseas. Reported revenue and profit growth rates have been grossly depressed as a result.

However, if you dig a little bit deeper into the numbers, it's as clear as day that Priceline is growing quickly. Last quarter, the company's reported revenue grew by only 7%, but if you adjust for currencies, it grew by a much more robust 22%. Meanwhile, the company's platform ended the quarter with more than 820,000 bookable properties, up 38% over the year-ago period. 

Traders can't seem to wrap their heads around the disconnect between reported numbers and operational (sans-currency) ones. Shares have already fallen more than 20% from recent highs, and they're currently trading hands for around 23 times trailing earnings. Given that the company is expected to grow its earnings by nearly 15% annually over the next five years, I'd say the shares are already attractively priced. If Mr. Market has another fit and sells off shares even more, I'd be happy to add to my already sizable position in this great business.