Sci-Fi blockbusters, the unheralded hero is always the guy or girl no one pays attention to.
Han Solo was the captain of the Millenium Falcon, but Chewie made all the repairs; Han spent most of his time barking and running around like a headless chicken. Chewbacca, though loud and furry, always kept his cool to make sure the Millenium Falcon was operational. That, and the fact that Chewie was over seven feet tall and strong as an ox makes him a shoe-in for the most incredible of sidekicks.
Indiana Jones on multiple occasions throughout the flick. Short Round was his getaway driver, bodyguard and ultimately saved Dr. Jones from a crazed child with a voodoo doll and the black sleep of Kali. Most importantly, he kept the audience's attention away from Kate Capshaw's annoying whining.
Hit Girl from "Kick-Ass" She's so awesome that it seems unfair to put her in the sidekick category. Hit Girl could actually have her own flick. Her body count alone warrants some sort of incredible sidekick award. While Kick-Ass spent the majority of the flick getting his face smashed in, Hit Girl was kicking ass and taking names and kicking more ass. She was an expert martial artist and a weapon-wielding terror. She single-handedly brought down an entire gang and she's only eleven!
Sam from "The Lord of the Rings" Originally showcased as a bumbling, fat idiot of sorts, Sam really stepped up to saved the day. If he wasn't carrying a lethargic Frodo on his back, he was fighting Orcs and huge spiders, or preparing a home cooked meal for the adventurers. No, he didn't have the master skills of a swordsman or magic, but the guy just wouldn't quit. The people of Middle Earth owe him a thank you. So do the moviegoers. If it wasn't for him you'd have to listen to Frodo crying three hours a movie.