Zack Fair, the thoroughly Adorkable protagonist in the Final Fantasy VII prequel Crisis Core, is enthusiastic, bouncy, and friendly to the point that people start sticking him with the nickname "puppy".
Snow Villiers from Final Fantasy XIII is not a little boy at all — in fact, he's a positively huge rough-and-tumble looking guy — but he's got the personality pretty much down pat.
Inazuma Eleven, Endou Mamoru is probably the happiest of the major heroes in the Raimon Academy and Inazuma Japan National. His happy trait and Heroic Spirit are what drive the team to victory. Moreover, he almost never angst after the first game.
Kid Icarus: Surprisingly, Pit, to the point that even when the game gets dark and serious, he's incredibly difficult to take seriously.
Sora, of the Kingdom Hearts series can be relentlessly cheerful. He pretty much has to be to be able to keep up with a pair of classic Toons as his sidekicks.
Ventus is just as adorable and cheerful as Sora, but in less of a "hyperactive puppy" kind of way and more of a down-to-earth, gently smiling fashion.
Arguably Louis from the original Left 4 Dead is another, perpetually optimistic flavor of keet, always hopeful, trying to keep the team's spirits up and looking at the bright side of things in the middle of a Zombie Apocalypse.
Conrad Verner from Mass Effect, a hyperactive, hyperenthusiastic Fanboy who keeps trying to impress Shepard. If you're not careful in dealing with him, his enthusiasm can get him killed.
Claus from Mother 3. For the single chapter he's alive, that is.
Teddie from Persona 4. Tiny, loud, hyper, cheerful and the instigator of most of the homosexual things in the game.
More so then his anime counterpart, Barry/Pearl/Damion from Pokémon Diamond, Pearl, and Platinum.
Griff Simmons from the SSX Series fits well into this.
Sonic the Hedgehog: Charmy Bee fits perfectly into this trope, as he is often energetic, playful, and very scatterbrained. Of course, his constant buzzing can be annoying sometimes.
Super Mario Bros.: Mario definitely fits as one of these, with his cheerful YAHOOs and WAHAHAHAs.
In most of his incarnations, Link is a rather serious young person. By contrast, The Legend of Zelda: The Wind Waker's Link is cheerful, upbeat, and downright silly at times. He can still go toe to toe with the baddest of the bad, but he was also once turned into a human pancake.
Cadet Ellis (no relation to the Ellis above) from Vindictus. Makes it all the more of a Player Punch when he eagerly runs off to prove himself and gets brutally killed by a giant goblin.