Are you looking for some exciting growth stocks to put in your portfolio? While some stocks may have risen to absurd valuations, there are still deals out there, especially for long-term investors. Three stocks that are doing well this year and that arguably still look cheap are Vertex Pharmaceuticals (VRTX 0.47%)Carnival (CCL 0.60%), and Alphabet (GOOG 1.25%). At less than 25 times their future earnings and plenty of growth potential, these high-flying stocks could just be getting warmed up.

1. Vertex Pharmaceuticals

It has been a strong year for Vertex Pharmaceuticals stock. Up around 25% year to date, it's trading near its 52-week high as the business has continued to do well this year with revenue rising 13% year to date and more growth still on the horizon.

But despite its gains to date, this healthcare stock could be heading even higher in the future. That's because the business is getting bigger and more diverse. Today its revenue predominantly comes from its cystic fibrosis (CF) drugs -- but that could soon change.

A big catalyst could be coming soon as the Food and Drug Administration will make the first of multiple decisions on gene-editing therapy exa-cel before the end of the year. It's a treatment for sickle cell disease and beta thalassemia that could be priced at nearly $2 million. If it gets the green light, that could lift the share price for both Vertex and its development partner, CRISPR Therapeutics.

Vertex generates a strong profit margin of around 35% and with more growth catalysts to expand its operations beyond its already leading CF franchise, which has no significant competitors, the stock looks poised to go much higher in the long run. Last year, its sales came in at just under $9 billion.

At a multiple of 23 times its estimated future earnings, it's also not a whole lot more expensive than the average stock on the S&P 500, which trades at a multiple of 19. For the high margins Vertex generates and some promising growth ahead, it warrants trading at a significant premium and it's still a cheap-looking stock today.

2. Carnival

Cruises are in strong demand this year, so much so that cruise ship operators such as Carnival are able to raise prices without much concern that the moves will hurt business. What's attractive about the cruise business is that it caters to an older, more affluent type of customer. This includes retirees, who may be in better financial shape and have more discretionary income at their disposal than other types of customers.

Last month, the company reported $6.9 billion in revenue (an all-time high) for the period ending Aug. 31, which was a 59% improvement from the prior-year period. More importantly, its operating profit of $1.6 billion was considerably better than the $279 million loss Carnival incurred a year ago.

One thing risk-averse investors are worried about is the company's debt. But with stronger financials as the business recovers from the effects of the pandemic, the company is committed to paying that down and plans to reduce it to less than $33 billion by the end of the year, down from a peak of $35 billion. And with better cash flow, there will be less of a need for the company to rely on stock offerings, as it has in the past few years.

The company is on a much better path with the industry returning to normal and travel demand looking strong again. The travel stock has increased 37% in value this year but with a forward price-to-earnings (P/E) multiple of only 11, it's still a fairly cheap investment overall.

3. Alphabet

The hottest stock on this list is Alphabet, the company that owns YouTube and Google. Tech stocks have been surging this year due to the growing popularity of artificial intelligence (AI). Alphabet has developed a chatbot, Bard, a rival to OpenAI's ChatGPT, which Microsoft has invested billions into, as AI is likely to be the next big battleground between these two tech giants. Alphabet is rolling out AI-powered tools for its Office software, and Microsoft is doing the same with many of its products.  

Alphabet is a promising AI stock but it's not trading at an obscene valuation. At a forward P/E of only 20 (Microsoft is at a multiple of 30), it's not hard to make a case that this is potentially an undervalued stock, especially given the potential it has in AI.

One thing that's likely keeping investors hesitant, however, is the antitrust case the Federal Trade Commission recently launched against Google for monopolizing search, and what that could mean for the future of the business, including how dominant the search engine might still be in the future.

But Google has built up such a strong brand over the years that it's hard to imagine a scenario where it isn't the go-to option for people looking to search -- or to "Google" -- something. With close to $300 billion in annual revenue and a profit margin of over 21%, this is an excellent business to invest in for the long haul.