Without further delay, here are what I consider to be the top seven:
Chewbacca (Star Wars)
I would argue that Chewbacca is the greatest science fiction sidekick in film history, but I'm sure those reading this will disagree. But, given that he's a walking carpet with fangs, speaks in a bizarre grunting language that only Han Solo and Yoda seem to understand, and can pop the head off a grown man with his pinkie finger, I think he deserves to be here. Chewbacca is kind of like what a wolf would be like if it walked on two legs. Awesome? I think so.
Spock (Star Trek)
The only true rival to Chewbacca, in my opinion, Spock is sort of like the science fiction version of Legolas, only not nearly as cute. It would be hard to imagine Star Trek without Spock. What would Captain Kirk do without his half-human, half-vulcan, logic-spouting machine? He'd probably be dead and we wouldn't be talking about the guy as if he were real. Spock is like Kirk's exact opposite, and that seems to be why he functions so well as a character.
There's something astonishing about Zoe as a character. While some have criticized Whedon for making her a subservient woman, I see a strong, loyal female figure who follows Reynolds not because he's a man, but because he is and always has been her superior in military rank. And she seems to know exactly how to put up with Reynold's crap, like all good sidekicks should. Smart, witty, and damn good with a gun, Zoe is one of the best female sidekicks in science fiction history.
Professor Arturo (Sliders)
John Rhys Davies is amazing. If that isn't enough to put Professor Arturo on this list, then consider that Arturo was, by far, the best character on the show, so much so that his death drove the quality of Sliders right into the garbage bin. Arturo was smart, opinionated, and yet strangely lovable. His death was a shock for a damned good reason.
Starbuck (Battlestar Galactica, the new version)
Some may argue with me about whether Starbuck qualifies as a sidekick, but she needs to be on this list due to how awesome of a character she was in the re-imagined Battlestar Galactica. Not only is she a hell of a pilot and a bit of a badass, but Starbuck also has a remarkable fate that leads her on an emotional roller coaster to discover Earth. Watch the show and you'll understand why she's awesome.
Al Calavicci (Quantum Leap)
I wonder what it would be like to have a holographic projection of my best friend following me around as I'm thrust through time into other people's bodies. Would it be fun? Maybe. If Al were following me, though, I suspect it would be an interesting journey. This show is one of my Grandmother's favorites, and I can see why. Al is a fun character played by and equally fun actor (Dean Stockwell, who actually plays Caval on Battlestar Galactica).
Dana Scully (X-Files)
Last of this list is another character who might not be considered to be a sidekick. Scully has a remarkable independent attitude in the series, but makes it on this list primarily because she does act as a logic machine for Mulder--sort of like Spock does for Kirk. She knows how to deal with dead bodies, gets abducted by aliens, and sees a heck of a lot of strange stuff, but still manages to be a disbeliever right up until two steps from the end. That takes guts.
And there you have it. Anyone you disagree with? Who would you replace and why? Let me know in the comments!