Waldo Butters from The Dresden Files. If you've read the books, you know why. His growth from disposable sidekick character, to something significantly more, and his personal motivations for doing so, are some of my favorite character developments in writing.
The Lava Monster from Samurai Jack, Season 1 Episode 10. I cry every time I watch this episode, because this character is just so fucking awesome. He totally upstaged Jack in his own tv show. Just, everything about him, the performance by the voice actor, all of it. Fucking fantastic.
The friar guy from Van Helsing (played by the actor in Iron Fist as papa Meatcham). My god I loved this character. He was comic relief, but he was COMPETENT comic relief. He always had the thing the hero needed to save the day, even had his own dramatic badass moment where he's swinging on a rope across a bottomless pit to grab the McGuffin, in the middle of a thunderstorm, catches it, and hurls it to the hero to beat the Bad Guy. Hell, he even gets laid, and the hero didn't even pull that off. He was just a delight every time he was on the screen.
Bicycle Hero (I forget his specific hero name in One Punch Man). He knows he's not super powerful. He knows he will likely die fighting the things they are sent against, but he still goes anyway. Because he chose to defend others, to his last breath. And he will fight until that last breath, no matter how futile. Because to turn away is to turn his back on those he swore to protect, and he'd rather die than do that. That scene of him in the rain, facing off against that Fish King character, fucking awesome.
Leto from Sense 8. Holy fuckballs do I love this guy! xD First off, the actor playing him is awesome. He's so damn hilarious, and seems to be genuinely having a blast playing this sort of comic relief character in the show. But even while his character is mostly played for laughs, there are some really deep emotional threads working through his story, and one scene, where he stops running from himself, and faces up to his problems, that was just fucking great. It was simultaneously hilariously over the top, and awesome at the same time. Plus, I genuinely love his relationship with his lover. The two of them have great chemistry on screen.