Guess what -- becoming a millionaire may not be a mere pipe dream for you. If you have some meaningful sums to invest regularly and a lot of time, it's almost easy to become a millionaire. And if you don't, investments in some carefully selected stocks could get you there in short order.

Here's a look at three companies with great long-term growth potential.

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1. Costco Wholesale

Warehouse retailing giant Costco Wholesale (NASDAQ:COST) has been a success story for a long time, and that doesn't seem like it's going to change anytime soon. The company recently had 803 warehouses, 558 of which were in the U.S. and Puerto Rico. In its last reported quarter, its revenue rose nearly 17% year over year -- amid a global pandemic.

Costco's business model is a bit different from the traditional big retailer, because it charges an annual membership fee to customers, which delivers more than $3.5 billion annually. It also maintains a reputation as a good employer, paying higher average wages than its peers, and enjoying a low employee turnover rate of less than 6%, per a 2020 Business Strategy Hub report. It aims to do right by its customers, as well, capping its markups at 14% or 15%.

The stock has surged, nearly doubling in value over the past three years, so it's not exactly a screaming bargain at the moment. If you want to buy, you might add it to your watch list, waiting for a lower price, or you might buy a small initial position now, with the goal to buy more later. Those who own shares can enjoy some dividend income that may look puny, with a recent yield of 0.8%, but note that every few years, Costco has issued a special bonus dividend. The last one was this past December, and paid shareholders a hefty $10 per share.

2. Boston Scientific

Boston Scientific (NYSE:BSX), a specialist in medical devices, is looking attractively priced at recent levels. The company boasts more than 13,000 products and serves around 30 million patients annually. It employs some 36,000 people worldwide and rakes in more than $10 billion annually, while investing about $1 billion in research and development that can help grow revenue streams. Its offerings include stents, pacemakers, catheters, and heart valves.

The ongoing pandemic has created a giant headwind for Boston Scientific, with fewer people going to the doctor and many procedures getting postponed. This is not a permanent problem, though, so business should pick up considerably once much of the world is vaccinated and we eventually put COVID-19 behind us. That's not all, though -- Boston Scientific is also setting itself up for further growth by developing new products and by acquiring other companies that can bring new therapies and areas of expertise.

3. Intuitive Surgical

Another medical company worth considering for your money-making portfolio is Intuitive Surgical (NASDAQ:ISRG), a giant in the robotic surgery arena. Its da Vinci surgery systems cost between $500,000 and $2.5 million apiece, roughly, and the company has sold a lot of them: There are more than 5,800 installed worldwide, and they have performed more than 7 million procedures. But wait -- there's more! Intuitive Surgical clearly makes a lot of money with the sale of each system, but each system also generates a lot of recurring revenue, from supplies and service contracts.

There seems to be plenty of growth on the horizon for the company, as it rolls out machines capable of doing additional kinds of procedures and as more hospitals buy systems.

With the company's stock trading at price-to-earnings (P/E) and price-to-sales (P/S) ratios well above their five-year averages, Intuitive Surgical appears overvalued. As with Costco, you might wait for a pullback or buy only a portion of the shares you'd like to own, hoping for a lower price later on.

These are just a few of the many promising growth stocks that exist. Some more reading and research will likely turn up additional candidates for your portfolio -- just be sure to park your hard-earned dollars in companies that are strong and growing and also are reasonably or attractively priced.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.