With the S&P 500 index up by 65% over the past year, and the Dow Jones Industrial Average hitting fresh record highs, it might seem like the entire stock market is too expensive. Sure, some high-flying tech stocks have pulled back, but most of the popular names are still trading for multiples of where they were a year ago.

Fortunately, there are several real estate investment trusts, or REITs, that are not only cheap, but could deliver fantastic returns for long-term investors who get in now. Here are three that I own in my personal stock portfolio that I'm considering adding to at their current price levels.

Family walking through a mall.

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A leader with a massive growth opportunity

Digital Realty Trust (DLR 2.06%) owns and operates a large portfolio of data center properties located around the world and is one of the largest REITs of any kind in the market. Unlike the other two I'll discuss here, Digital Realty wasn't heavily impacted by the COVID-19 pandemic. In fact, the lockdowns and remote work trends dramatically increased the volume of data flowing around the world.

Like most so-called "stay-at-home" stocks, Digital Realty has pulled back considerably since we started to get some light at the end of the tunnel. Shares are nearly 20% lower than their 2020 high.

However, it's important for investors to realize that the long-term trends in the data center space are still strong. The gradual rollout of 5G technology around the world, the surge in internet-connected devices, and the growth in data-heavy technologies like autonomous vehicles and augmented reality are likely to keep data center demand rising for decades to come. Patient investors who add Digital Realty to their portfolios now could be in for years of outperformance.

The right kind of retail to invest in

Unlike Digital Realty, STORE Capital (STOR) was heavily impacted by the pandemic. Specifically, STORE Capital's primary focus is on single-tenant properties occupied by service and retail tenants. And about one-third of the company's properties are occupied by tenants in industries like movie theaters, family entertainment centers, fitness centers, day cares, and other properties that were largely forced to shut down or operate at a greatly reduced capacity for much of 2020.

However, the recent news has been encouraging. STORE's rent collection has steadily grown from 70% of billed rent at the height of the pandemic to 93% in February. Nearly all of the company's properties (except for a few theaters) are open for business. And STORE expects to be in all-out growth mode in 2021 with more than $1 billion in acquisition volume.

With shares still about 15% below their pre-pandemic high and a well-covered 4.2% dividend yield, STORE is a rapidly growing REIT that should produce an excellent combination of growth and income.

This collection of old Sears properties could be worth billions

Seritage Growth Properties (SRG 0.32%) was specifically created to buy a portfolio of properties occupied by Sears and Kmart stores. Of course, nobody thinks owning a Sears is a good investment these days. But that's the point.

Seritage owns a total of 183 properties with 26.5 million square feet of space and plans to gradually convert most of them into premier mixed-use real estate. And the early results have been impressive, with completed and released projects generating about four times the rental income of their previous (Sears) tenants. Seritage has only completed redevelopment on about 8.5 million square feet of properties that it owns, so it's still in the early stages. And it hasn't even touched most of its large-scale, premier (highest-potential) properties yet.

Currently, Seritage isn't profitable. And this isn't surprising -- after all, large-scale redevelopment costs money, and less than one-third of the company's real estate is currently generating rent. But the value-creation potential is enormous, especially when it comes to Seritage's most promising properties. With a market cap of less than $900 million, Seritage could multiply several times over if it can successfully execute on its vision.

Don't expect quick profits

To be perfectly clear, I'm suggesting these as attractive real estate stocks for long-term investors. I have absolutely no idea what they'll do over the next few weeks or months, and if there are further interest rate spikes and/or delays in reopening, investors could be in for a turbulent ride in the short term.

Having said that, I'm quite confident that investors who buy at these levels and hold for the next decade will be very glad they did. Invest accordingly.