Milo in Jonathan Kellerman’s Alex Delaware novels. I’m a little sick of Alex (always picking at his food) and Robin doesn’t do much for me (or Alex, apparently) anymore. But if Kellerman wrote a book with Milo as the main character, I’d read it.
Also, TJ in Lawrence Block’s Matthew Scudder novels. This is how Block handled the emergence of new technology, which would be really out of character for Matt. He introduced TJ, the genius techno-sidekick.
Agent 99 (Barbera Feldon) from “Get Smart”…
Gorgeous, (And ever), great fashion sense (Gun always matched outfit), always getting Smart out of trouble, and that little “eye roll” she did when Smart did something/said something bumblish…
Regards
FML
Sure, I’d enjoy many of the sidekicks above if I were dealing with Orcs, Imperial troopers or the like, but for serious help in today’s real world, I’d love to have Travis Magee’s incomparable Meyer, to whom the ladies flock, in whom children trust, and governments consult.
Note: Dr. Meyer is a retired economist, and Mr. MacDonald earned an MBA from Harvard in 1939
Mouse in Walter Mosley’s Easy Rawlins stories.
Does Emma Peel count as a sidekick? 'Cuz nobody is cooler than a high-kicking Diana Rigg.
Leela.
“Discussion is for the wise and the helpless. I am neither.”
Sgt. Detritus from the Discworld series always seems to come in handy.
Geez, no one’s mentioned SPOCK yet?
I need Spock, I really do. My computer insists on doing weird stuff.
OR Agent 99.
A curse on both your houses. I came in here specifically to mention him, and you guys stole my thunder.
But yes, another vote for Hawk. He is the very definition of cool. And I feel a bit like Susan does about him: he’s a very, very dangerous man, but I’d have nothing to fear from him. He’s a man of honor, even if his particular code doesn’t completely line up with what’s legal.
I thought of naming Hawk, but I didn’t because I don’t think he counts as a sidekick. Certainly he would not think of himself as one, and if a male were foolish enough to call him one in his presence, well, there’d be several very uncomfortable moments in store for that foolish man. Hawk and Spenser are, well, complex. They’re blood brothers, certainly, who have an unspoken agreement never to oppose one another and who happily cooperate when either needs help. Hawk may more often be the helper, but that’s probably because he less often needs help than Spenser does.
(I mean, really, does anyone think Spenser has half a chance of winning if he actually had to throw down with Hawk?)
Bullwinkle.
Just don’t forget to offer him one of your fresh-baked muffins.
I agree with all your points about Hawk as far as how his character is written in the books, including a win for Hawk in a throwdown with Spenser. However, his function within the story is definitely that of sidekick – he mostly comes along to help Spenser out when he needs it, the very definition of a sidekick.
For a moment, I thought you meant Inspector Clouseau’s Cato!
Would that be Leela from “Dr. Who” or Leela from “Futurama”? "Cuz I can picture either one of them speaking that quote.
Now if I were living in mid-70s L.A., and in dire need of some discreet investigative work, I’d probably want to place my trust in Bosley before I let any one of “Charlies’ Angels” handle my case. 
Do Morpheus, Trinity, and Tank count?
If not, my vote goes to Chloe O’Brien.
Bastard! You stole my idea of Meyer. I would also nominate Clete Purcel from the Robicheaux character series by James Lee Burke.
Ooooh. Good call.