If you’ve been collecting comic books since you were a kid, now is the time to list them on eBay. Blockbuster movie franchises from Marvel and DC have made superheroes more popular than ever, and characters that were once only beloved by die-hard comic fans are now mainstream. Here are some of the rare issues that may have been gathering dust—and value—in your attic for years.

1. Action Comics No. 1

The inaugural issue of Action Comics marked the first appearance of Superman and helped kick off the superhero genre. In 2014, a pristine issue of the 1938 comic, with its original price of 10 cents still on the cover, sold on eBay for $3.2 million, making it the most valuable comic book of all time. Action Comics No. 1 also holds the record for second-biggest comic book sale, with a copy previously owned by Nicholas Cage bagging $2.16 million in 2011. It’s believed that 50 to 100 copies of this first issue are still out there.

2. Amazing Fantasy No. 15

Before Spider-Man became the star of multiple comic books series, TV shows, and movie franchises, he was a special character introduced in issue No. 15 of Amazing Fantasy. The comic’s publisher was so underwhelmed by Stan Lee and Jack Kirby’s character that he only agreed to feature him because it was the series’s last issue. But the web-slinging hero turned out to be a hit with readers after he debuted in 1962, and he remains so popular today that a private collector paid $1.1 million for his first comic in 2011.

3. Detective Comics No. 27

A year after Superman hit the scene, Batman made his first appearance in the 27th issue of Detective Comics. In 2010, an anonymous buyer purchased a well-preserved copy of the 1939 comic for $1 million in an online bid. According to experts, 100 to 200 copies have survived to the present day.

4. All Star Comics No. 8

You wouldn’t know it by looking at the cover, but issue No. 8 of DC’s All Star Comics marked Wonder Woman’s first appearance. The story centers on the Justice Society of America, but it also features the origin story of one of the fiercest superwomen in comics. A copy sold for $936,223 on eBay in 2017.

5. X-Men No. 1

In 2012, the debut issue of X-Men from 1963 sold for $492,937 at auction. The near-mint copy earned a 9.8 out of 10 on the CGC scale, the metric used by collectors to determine the quality of vintage comics. The issue introduced Cyclops, Beast, and Magneto (Wolverine wouldn’t show up for another decade).

6. Tales of Suspense No. 39

Iron Man was considered a B-list Marvel superhero for years—until 2008, when the film adaptation thrust the character into the spotlight. The buzz around Iron Man made his debut issue from 1963, Tales of Suspense No. 39, one of the best-selling comics from the era when it sold for $375,000 in 2012.

7. Marvel Comics No. 1

Today Marvel seems to dominate every realm of pop culture, but the behemoth had to start somewhere. Marvel Comics No. 1 came out in 1939, decades before the X-Men, Spider-Man, and the Incredible Hulk were conceived. But the inaugural issue from the company that would eventually become Marvel Comics did feature an early version of one of the brand’s core characters: the Human Torch. In 2001, a copy of the comic book sold for $350,000.

8. The Incredible Hulk No. 1

The Incredible Hulk’s first comic was listed for 12 cents when it hit stands in 1962, but today it can earn collectors a few hundred thousand bucks. In 2014, The Incredible Hulk No. 1 sold for $320,000 at auction. This early version of the antihero was gray, but due to printing press issues giving him a greenish tint, the creators eventually decided to make the Hulk green on purpose.

9. All American Comics No. 16

The Green Lantern’s origin story is told in issue No. 16 of the DC series All American Comics from 1940. The issue is considerably rarer than other important comics from this era, with just 21 to 50 thought to remain in existence. Those factors led to a copy of the issue fetching over $200,000 at auction in 2013.

10. Suspense Comics No. 3

The third issue of Suspense Comics—a short-lived horror/thriller title—became the most valuable non-superhero comic book ever when a copy sold for $173,275 in 2015. The provocative cover (featuring a bound young woman about to be slain by hooded figures wearing swastikas) meant that some vendors opted not to sell the issue when it first came out in 1944, and today surviving copies are scarce as a result.