Morte from Planescape: Torment. For a jackass floating skull he could kick all kinds of ass, especially when you got him sharper teeth!
From Timesplitters: Future Perfect:
Best: Amy. You never need to rescue her, she doesn’t get in the way, and she’s perfectly capable of defending herself. (However, Jo-Beth Casey is cuter.)
Worst: Harry Tipper. Can’t fight his way out of a bag, spends most of the mission in drag flirting with a guard (who apparently doesn’t care about the lip hamster Tipper is rockin’), and makes you try and snipe dozens of guards while he goes and steals uniforms.
I thought about Navi at work today. She drove me up the wall.
I am surprised that nobody has mentioned these two guys yet… noy sure if they count because you do get the play as them eventually…
Clank from Ratchet and Clank. Yeah, it was a fun, mindless game, but he was a good sidekick!
Daxter from Jak and Daxter. Probably one of the funnier ones out there.
Yeah, I live for platformers.
Hampshire are you sure you’re not thinking of Ico? I could be wrong, I don’t remember a lot of POP SOT, It was so long ago, so I could be wrong.
I can’t quite remember or find it, but it goes something like this:
Pink: “Well, against all odds kinds, priests, and nobles all lost and now merchants rule the world. Ha! And can you believe there are still people who believe the world was made in seven days?”
Christof: “The world was made in six days, Pink.”
Ultima. My old friends Iolo, Shamino, and Dupree. I can say no more.
There was something in there, too, about peasants choosing their kings. 
Seconded. I wondered about the melee abilities myself. But, for the life of me, I couldn’t understand why an assassin droid couldn’t hold one rifle in each arm.
Try Knight II. The robot G0T0 is completely worthless. You can’t avoid getting him in your quest, but you can play the entire game without ever using or interacting with him from the point he joins you. He plays a big part in the plot, but it’s all in cutscenes.
Best sidekick ever: Dog, from Half-life 2. You only get to fight alongside him for a few breif parts of the game, but when he’s there, there’s very little need for you to do anything but watch as he rips up large pieces of scenery and throws them at the bad guys. Alyx isn’t bad either - competent with a gun and able to defend herself, as well as do useful things like open locked doors and reprogram auto turrets.
No. Unfortunately for me I bought that steaming pile of crap in a box, but could never make it run. I am still very bitter and will never buy another thing that Romero is a part of.
Occcasionally? What game were you playing? I looked in the other direction and she was all “HELLLLLLP MEEEE!”
On the plus side, tho’, if she’s in her skirt outfit and you’re waiting to catch her, and you look up before she jumps she yells at you for being a pervert 
Best sidekicks, tho? Billy/Rebecca in Resident Evil 0. At least they shoot things when you’re not playing one of them.
He was useful in Sonic 3 and the lockon game Sonic and Knuckles.
Harborwolf, that webcomic goes on my list of webcomics to read the archives of.
What can I say, Ashley just must feel more secure while I’m escorting her.
And yeah, getting called a pervert is fun. The first time it happened wasn’t even on purpose. I think she had gotten knocked down or something and I got a look up her skirt. I was like, “hey, I’m saving that cute little butt and that’s the thanks I get?”
In Arcanum, best sidekick was the dog. You need to save his life from a greedy master in a town before the sun goes down (hard to do unless you know exactly where to look for him), but once he’s yours… He kicks all -kinds- of butt in melee combat (heck, he bites robots for damage. Very impressive)
Worst? Same game, Virgil. (I think that was his name)- first NPC you meet. Great storyline, good healer… Unless you’ve decided to follow tech instead of magic. Then he’ll consistantly try to heal you and fail in combat, never realizing he should be doing something… ANYTHING… Vaguely more useful.
(Besides, the tech healer was more cute, and would actually resurrect you if you died, assuming she had a ressurect kit)
I don’t know what you’re doing wrong. The only time she was taken from me was when she was using the crank on the upper ledge. Even then she barely got out the word “help.”
Wolfian, glad you liked it. Vg Cats is my favorite webcomic. Scott Ramsooair is brilliant. 
I second the nomination of the ant-lions in Half-Life 2:
“Damn! I need cover from those machineguns! Go get 'em, Ant-Lions!”
“Damn, there’s a guy WAY up on top of that tower shooting at me. Go get 'em, Ant-Lions!”
“Hmm… I wonder what’s down that corridor… Go take a look, Ant-Lions!”
“Hey, that laser tripwire is attached to a mine I could easily shoot from here. Buuuut, bullets ain’t free… Go set off that mine, Ant-Lions!”
I would also add, for your consideration, the entire cast of Baldur’s Gate II’s sidekicks, with the exception of the de-winged elf chick and the generic human chick whose estate you have to go liberate from trolls or something.
Another vote for HK-47 as the best sidekick. I forced myself to play the whole game with him in the party just to hear what he had to say. Hearing him call people “meatbags” was worth having to haul a useless non-Jedi around for 20 hours.
I am permanently traumatized by this stupid owl. I was playing Ocarina of Time, and the owl showed up, and I actually flinched.
Best: Glottis from Grim Fandango.
Ok, Glottis is second-best…HK-47 is the best, or at least the coolest.
My character from that game would challenge you to a duel for dissing his sweetie!
Actually I liked Aeirie, the de-winged elf, for the fact that as a cleric/Magic user, she became a spell casting machine at higher levels. Mobile artillery combined with a field hospital.
The best sidekick from that (and any) game still has to be Minsc (with boo). Good in a fight, and had some truly hilarious dialog.
The worst? Any of the escort missions from Morrowind. Nothing like weak characters who are willing to seek out/ attack monsters, as well as actively getting in your way in a fight!