These are show I wish became popular enough to warrant more of each, although some did last a long time, its just they never garnered that much a following. There probably are fanbases I am not aware of, this is just my quick look.
This may sound strange, but most of these are pretty much tied for number one, at least to me, I just love 'em, but I may be wrong, some of these may just be garbage, its just my interpretation.
Runner up: Tales From the Crypt Keeper- Done in a similar heavy inked fashion as Swat Kats, TFTCK is an animated kids show spin off of the classic HBO series. Cryptie plays host as always, except these stories are more about monsters and lessons for kids than psycological horror. Would've made it on, just, I didn't grow up with it, and I haven't seen enough of the show to know how well it holds up against the other contenders.
10. Jackie Chan Adventures- Not the first show based around a popular character, but definitely one of the best, and possibly last. While the titular actor is not actually the voice of himself, he does pop in at the end to deliver some background about his life as a martial artist, sort of relating to the story. The first season is centered around mystical stone talismans that grant a power to the wielder. Each one is engraved with one of the 12 animals of the Chinese Zodiac and acts as a 12 piece key to unlocking a powerful demon named Shendu. Each season centers around a similar premise, from Shendu seeking to release his demon brothers, to Oni masks bringing forth various dark ninjas known as Shadow Khan. There are even a few "filler" episodes such as Jackie in the old west, and Jackie and a Chi Vampire. The show has wit and charm, and some decent voice casting. Clancy Brown seems to be used a lot, but its not noticeable. Check it out if you're a fan of Jackie Chan, Asian Fantasy, or over the top stereotypes.
9. SWAT Kats- Essentially Hannah Barbara's last hurrah, SWAT Kats went into some really dark places, and not just in tone. The style is a mixture of heavy ink comics and Anime. From the guys behind Scooby Doo and Tom and Jerry, this was surprisingly morbid. The episodes I point to especially are the one's involving Doctor Viper, a half-reptilian mutant cat with a penchant for trying to destroy the civilized world to erect his own utopia of mutated plants and animals, you know, that stuff. His introduction episode has him turning a fellow supervillain into a giant bacteria monster (onscreen transformation, pretty brutal) and said monster devouring cow, and even a subway full of people (I shit you not). Even Viper's origin story is morbid. He was a lab assistant who stole a formula to mutate plants, fell down the stairs getting doused in the stuff, DIED, and regenerated as a mutant. The show has good animation, good voice acting, classic yet not overused comic book plots, and a killer intro.
8. Xiaolin Showdown- This is actually a good one for Bronies, as the humor is very similar. The main characters are chosen bearers of special elements and have great chemistry with each other, working for a wise master with their pet dragon to defeat enemies and collecting magical artif- WHAT THE HELL!!!!! Ok, ok, probably a coincidence. So the strong blonde one has a southern accent and always wears a cowboy h- HOLY SHIT! Um, um, The main character is voiced by Tera Strong and is the workaholic of the group, is pretty socially awkward, and is always seeking to please their master often getting in trouble trying to. . . What. The. FUCK! But, jokes aside, the show is pretty good, and has very humorous villains, my favorite being Jack Spicer, a boy robotics genius and main antagonist for the first season.
7. Dan VS- The newest one on the list, Dan Vs is about the titular Dan declaring war on minor first world problems like going to the dentist or getting caught in traffic. He usually blows things out of proportion, only to be proven right, like when his dentist (played by Mark "Mistah J Skywalker" Hamill) turns out to be a supervillain who plans on... go on, say it, I know you want to.
You: Take over the w-
M. Bison: OF COURSE!
Dan is really the best character, being that lovable asshole we would probably avoid in real life, but admire on screen. He is helped by his pushover friend and his secret agent wife (surreal). The Show runs on much more mature humor than Hub's other programming, showing blood, a death or two, and even one case of swearing (Dan quotes Shakespeare with "OUT, DAMN SPOT!"). I get the feeling it was green lit when Hasbro realized Hub was attracting a more adult audience, that could also explain the onslaught of nostalgic cartoons like Batman, Animaniacs, and Tiny Toons. Its been put on Hiatus, but Dan's VA says its not cancelled.
6. Digimon Frontier- So... this iteration of Digimon involves.... the kids turning into their Digimon- WAIT PLEASE COME BACK!
Yes, I know it sounds dumb, like something from a furry Digimon Fanfiction, but its actually handled surprisingly well. Kids who are having problems in their life are invited by a mysterious cellphone call to the train station, where dozens of kids turn out, and they are all transported to the digital world. The four kids we follow manage to become the new digidestined and have to use their spirit evolution to stop other similar ranked digimon from consuming the digital world. It retains the dark tone the shows have been known for, even dealing with themes like failure in a surprisingly mature manner. And, the intro... SWEET CHRIST ITS AWESOME.
5. ThunderCats (2011)- A more mature update to the iconic 1980's series, ThunderCats is not unappreciated, but its lack of fanfare led to Cartoon Network Cancelling it. It really is an improvement, as much as I hate to dump on the classic. Animation, voice acting, everything... except one thing, does anyone else think Panthro's new design looks a bit too much like Jet from Cowboy Beebop?
4. Transformers Armada- Ok, I'm going to catch so much crap for this, but to hell with it, I like this version of Megatron better than Frank Welker's. This one has a sophisticated, intelligent voice, whereas Welker's was the exact same one he later used for Professor Viper, and you know what, it fit the Snake Cat a thousand times more. Some of it is blatantly trying to sell toys, like the Minicons being the prime focus, but it was actually a lot more grown up. I remember at one time, Starscream had a moral conundrum and switched sides, and after a heartfelt conversation with the show's lead human female, went back to the Decepticons. Never saw that in the original one. And it does address themes like betrayal and morality, it really does just confound me how it did this sticking to a Y7 rating.
3. Master's Of the Universe (2002)- A third update on a classic 80's cartoon series, MOTU is much like ThunderCats in the respect of updating everything, the most important being He-Man and Skeletor. Prince Adam is now a scrawny teen while He-Man retains his taller muscular build and amazing jaw-line. Skeletor drops the silly voice, and we actually find out WHY he has a skull for a face (yet they still don't explain how he talks without lips).
2. Spectacular Spiderman- I will address my only two problems with the show right now: They kept that stupid idea for AI tentacles with Doc Ock, and Electro without his mask looks ridiculous. Everything else is awesome, even better than the somewhat lackluster yet nostalgic 90's one. The voice acting is all star, featuring Crispin Freeman (Electro), Robert Englund (Vulture), Clancy Brown (Captain Stacy and Rhino), John DiMaggio (Hammerhead and Sand Man), Peter MacNicol (Doc Ock), and an especial shout out to Steve Blum's surprisingly good performance as the Green Goblin, yeah, Spike Spiegel is the Green Goblin, and he is awesome, just a riot to watch. The animation kind of reminds of me of FiM, owning its two dimensionality, and it FEELS like you're in a city, with individual buildings and streets brimming with people. It is sad with how short its run was, it was pretty damn good.
1. Baccano!- My God, this show is awesome. In my opinion, it deserves to be up with Death Note and Cowboy Beebop as the greatest Anime on Earth. The story is compelling, the characters are amazing, the voice acting is pitch perfect, and the animation is fluid and swift. The only problem anyone might have is its spacing. The story is completely jumbled up, like say, newspaper articles. It can be confusing, but you'll pick up on it eventually, and the ending is amazing, I just wish they continued it. The Manga goes on for quite a while, but the show has like only 16 episodes to it. I think the main reason its not popular is the fact its as jumbled as Man Of Steel (Which I also liked). So, if you're ok with being a little confused, and like the 1930's, thieves, assassins, mobsters, or alchemists, look it up. Voice acting is also really good, and the intro, jazzy and up beat, yet a little manic, much like the show itself. On an unrelated note, the show has a (perhaps unintentional) unique and fascinating interpretation of the Devil. I think the translators just mistranslated Demon to Devil, but what we got is pretty cool. This version of the Devil is actually not evil, and just gives humanity tools, which can be used to help or destroy humanity, which adds this deeply philosophical moral of "the only true evil is the one in our hearts" but I may just be thinking to hard about it. It is a pretty interesting concept, and he even says "I'm probably going to get blamed for this" after one of the Alchemists he helps make immortal goes insane, even though he had nothing to do with it.
I hope you enjoyed my list, and remember, its just my interpretation. Please comment on TV shows you feel don't get enough credit below, or disagree with me and tell me my list is bullshit, its a free country.