Lisa Simpson in The Simpsons. Marge as well, in a few cases, but she is just a bit too oblivious to what constitutes as normal human behavior to do any discrediting.
In Transformers Generation One, Wheeljack and Ratchet shared this role in the first season, Perceptor joined in as a third Smart Guy in the second season, and the third season saw Perceptor become the sole Smart Guy after Wheeljack and Ratchet's deaths in The Movie. The fourth "season" (really just a few episodes) introduced Brainstorm for this role, but the show ended before much could be done with him.
Kyle from South Park often gets this role when compared with the others boys, and even Matt and Trey have called him the group's "smart kid".
Walden from Wow! Wow! Wubbzy! fills this role on the show. As the theme song says, "he knows about science and books and art."
Sam Dullard of Rocket Power is a huge computer whiz and uses that knowledge to help the others improve their sports skills every once in a while. He has also skipped a grade.
Tako, the unofficial leader of the Sushi Pack, is the one usually called on to think of a plan to defeat the bad guys, and even has a standard "thinking routine". He also offers explanations of more complicated terms that come up in the show.
Wade Load of Kim Possible, a ten-year-old super genius who invents all of Kim's gadgets. Oh, and, he's voiced by Taj Mowry, who also played the titular character of a TV show of the Trope Name.
Raven has elements of this too, despite primarily being The Lancer. Of course, Cyborg also sometimes fills the role of The Lancer despite primarily being The Smart Guy, so it all evens out.
Robin, being the strategist and Batman's apprentice, can fill this role as well, especially when assessing new threats or being Mr. Exposition.
Winx Club made a half-hearted attempt to avert the "usually the technologically-minded character" aspect by having the girls mention that Musa and Flora get the best grades; nevertheless, the show kept using Tecna in the role of The Smart Girl. Timmy is also one for the Specialists, being the tech expert for them.
In the 4Kids version this turns a little racist; Flora's name is cut out of the best grades line, meaning that Musa, the Asian-inspired character, is the only one mentioned.
The sequel series has Mako, who doubles as The Lancer. He is the street smart and strategic one of the group.
In Futurama super-tech is so common that the Smart Guy is actually the only character capable of running the Planet Express delivery company, in the form of Hermes Conrad, a Level 34 beauraucrat and the team's Only Sane Man. Professor Farnsworth also counts, though more in a Genius Ditz / Reluctant Mad Scientist sort of way.
Flap Platypus in season 1 of Blinky Bill, in season 2 Shifty Dingo takes over the role and Flap becomes The Lancer. In season 3, Ling Ling the panda qualifies.
Blossom and Professor Utonium on The Powerpuff Girls both shows some moxie in the intelligence department, but they will often get Flanderized (Blossom as egocentric, the Professor as a haplessly overconcerned parent) to keep them from being too one-dimensional.
Twilight Sparkle takes the role in My Little Pony: Friendship Is Magic, though it's subverted more often than not due to her lack of real world experience to back up her vast book learning. She's certainly capable of some Awesomeness by Analysis however, along with some hardcore exposition.
In Teenage Mutant Ninja Turtles (2003), Donatello's intelligence rises sharply to the point where he can build just about anything within a day or two (it seems to vary on how soon the team needs it), and figures out how to adapt Utrom tech, along with almost all other alien technology. He's also the guy with the Simple Staff, and generally considered the Technical Pacifist.
Shy-but-sensible Austin of The Backyardigans, both in and out of character. Uniqua also tends to play scientific types, while more excitable Pablo is usually used to play with the concept.
Dotty, Pepper's cute little sister on Clue Club. She's a computer whiz (for 1976) and has science and forensic moxie. At age 13.
Pickles the Drummer, of Metalocalypse, although compared to his bandmates that isn't saying much. Although all of the bandmates have at least one area of expertise despite being catastrophically stupid otherwise, Pickles is implied to be very intelligent: he can play several instruments (and started a highly successful glam rock band as a teenager), understand complex mathematics well enough to explain them to Nathan, read and write music, and seems to have graduated college despite champion-level alcoholism. He might even be a genius, except that because of his implied-to-be-supernatural tolerance, he takes drugs the way other people eat potato chips, and his miserable childhood left him with a level of emotional immaturity that generally puts him on par with the rest of Dethklok.
