Green Arrow quickly became a fan favorite and rose to become one of the main characters from Season Eight onwards, though he became a slight Base-Breaking Character afterward.
Tess Mercer (Cassidy Freeman) was one new character from the show's later years that enjoyed widespread popularity.
Alicia Baker, a meteor freak with teleportation powers, was only supposed to appear in one episode, but despite being a Yandere proved popular enough that they brought her back for a run in Season 4, complete with a Heel–Face Turn.
There were quite a few fans who frankly preferred Isobel over Lana as Isobel was seen as a character who, while evil, was rather fun to watch, in a way similar to Lionel. Her Large Ham tendencies also made her entertaining.
Sheriff Nancy Adams was this trope for a lot of people. Although her first couple of appearances portrayed her as an Obstructive Bureaucrat who didn't trust Clark, her toughness and her ability to be completely unintimidated by criminals or the Luthors won her some respect pretty quickly. Then, as she spends more time in Smallville she starts to wise up to the fact there are indeed some weird and paranormal events happening in town, and gradually starts to trust Clark more, even if she still urges him to let the police handle things (this makes perfect sense since Clark is a minor and Sheriff Adams didn't know about his powers; she honestly thought she was protecting him and his friends). By Season 5, Sheriff Adams had developed a friendly relationship with Clark, and even urged him to consider the possibility of joining law enforcement full-time, a complete turnaround from her initial antagonism towards his vigilantism. Through it all, her toughness and her firm commitment to protecting the peace won her a lot of respect from fans... and her Deadpan Snarker tendencies certainly helped as well.
Kyla Willowbrook makes a huge impact in her one episode for her Anti-Villain status, chemistry with Clark, and Our Werewolves Are Different powers and has a lot of people who ship her and Clark and/or wish she had gotten more than one episode.
Non-malicious meteor freaks Jordan Cross (who has visions of people's deaths and tries to prevent them), Cyrus Krupp (who has Healing Hands and harmless delusions that he's an alien), and Sarah Conroy (who can bring people into a dreamworld and ultimately comes across as The Cutie) all have minor followings and appear on internet lists of notable One Shot Characters.
The Wonder Twins' sole appearance in the show caused them to be Rescued from the Scrappy Heap for many fans due to being portrayed as realistically flawed Heroic Wannabes who get some Character Development and use their powers more interestingly than they ever did in the cartoons.
Talkative LoonReality Warper Dr. Fate is one of the show's most beloved superheroes despite only getting one appearance. The other members of the JSA like Hawkman and Stargirl are pretty well liked as well.
The Freudian Trio Legion of Superheroes founders (especially Ascended Fanboy Garth) are all one-shot characters, save for Rokk, but their backstory, characterization, and status as the first live-action versions of their characters win them a lot of fans.
