This is probably one of the first you think of when you hear someone mention a hero named "Captain...?" The shield-slinger has been around for decades, and is just now apparently getting a fairly decent movie treatment.
For a while, he was Steve Rogers, then Bucky Barnes took over, then Steve came back and Bucky went to jail. Technically this leaves us with no clear Captain America as the movie is coming out, but I'm sure that will all be fixed up quickly.
Any way you look at it, the guy is popular with more statues and figures out there than any other hero on this list.
Captain Marvel (Marvel version)
This is one of the few "Captains" who actually has a military rank for his name. Granted, it's in the Kree army, but it counts. Mar-vell died in the very first Marvel graphic novel ever created called (surprise) "The Death of Captain Marvel".
The story did so well it paved the way for many more graphic novels over time. Unfortunately now every TPB is branded a graphic novel which cheapens the title. Read the original story in light of the comic books coming out at the time and you'll see why it was such an amazing story.
Captain Marvel (DC version)
This poor hero had a hard time of it for a while. When he first came out, DC included him in their rash of legal challenges against any and every hero who even remotely resembled Superman. Even though he was a popular hero with a lot of differences from the man of steel, DC won and the character spent years in comic book limbo. Ironically enough, DC bought the character and later brought him to his own series of stories that proved very popular.
He has fought Superman a lot over the years, though their titanic battle in Kingdom Come remains my favorite. In that one he truly cut loose against Superman and took him down, answering once and for all who would really win if the gloves were off.
One of those "funny animal" heroes, Captain Carrot really is a pretty cool dude. I remember reading that first issue as a kid and being hooked from that point forward. Spending years in limbo, they were brought back two years ago in a mini-series that ended up making them real animals in our world. They did get to come back in Final Crisis, but nothing has happened with him since.
To me, I think a Captain Carrot action figure would be a huge hit. The costume was cool and I'd love to see it in 3D as a figure, though I doubt he'll ever get one. Then again, if Animal Man can get a figure, surely some custom figure guy will try his hand at Captain Carrot and put him on Ebay!
Hey, tomorrow's my birthday, so if you're good at that thing and feel generous, it would be one of the coolest geek birthday presents I've gotten in a long time!
There are rumors he'll be a cameo in the upcoming Captain America movie. If he is, I highly doubt he'll show up in his awesome 70's outfit with the medallion and staff. Oh there are plenty of haters on the internet who hate that thing, but it beats out his later spandex outfit to me.
This character started out as Marvel's answer to Captain America for England, but he eventually made his way over the pond to team up with Spider-Man against Arcade in Murderworld. Years later he proved popular enough to lead a team called Excalibur (Marvel's attempt at a British version of the X-Men with a few mutants thrown in for the mix).
Known as "The Man From the Day After Tomorrow", Captain Comet showed up for several issues as the lead hero during the run of "Society of Super Villains". After that he was pretty much banished to guest-star-only status for over a decade.
Even though he's been in several books since then, he has yet to really make a long-lasting impression on many readers. Most of the titles he appears in tend to be canceled shortly after he joins the roster. It makes no sense to me though, because I think the guy is pretty fun to read about. Great costume too!
I still remember Micronauts #8 where we first saw this hero. Though the idea of a person becoming a hero to help in a situation and then losing that power isn't new (remember "Dial H for Hero"?) the way the character moved into his own series later on was a nice touch. Each issue would see a different person get the power and use it their own way. Sometimes they helped people, and once a cat burglar got it and tried to use it for his own selfish gains (it didn't end well for him).
The Uni-Power has even taken over a number of superheroes. Spider-Man was the first, then later the Silver Surfer, the Hulk, Sue Storm, and Daredevil all got their chance at unlimited power.
Another hero who got his "Captain" title from military rank, Captain Atom was originally a Charleton character that was bought by DC. One of only three that really made an impact in the DC universe (the other two are the Blue Beetle and the Question), Captain Atom is the only one of the three still the original character from Charleton.
The good Captain even made his way into a nice Justice League Unlimited story arch on television, working for the government to stop the Question and Huntress. He's recently rejoined Justice League International members Booster Gold, Fire, and Ice in Justice League: Generation Lost.