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troperville

Most incarnations of Superman's pal, Jimmy Olsen.
- Superman himself. The essence of his character is being a shining example for others to look up to.
Green Lantern Hal Jordan's younger brother, Jim Jordan.
Peter Parker. The fact that he's so nice is part of the reason his Woobiness is so pronounced in light of his crappy life and the irrational hatred he gets from those he helps.
Dick Grayson. DC Comics' official position is that he's the most beloved superhero in the community (yes, even moreso than Superman) and that almost any member of it would instantly drop what they were doing to help if he were in trouble.
- Tim Drake, Robin III is also a nice guy, especially in his early Robin Series. He took care of his girlfriend who was pregnant with her ex-boyfriend's child, and is good at babysitting kids. In the new DCU, he was also called a nice guy by Wondergirl.
Kim Pine from Scott Pilgrim may be a bitter Deadpan Snarker Grumpy Bear, but also a true friend of Scott, helping him with Sex Bob-Omb, despite things like being dumped by him in a pretty dickish way and, in volume 5, she demonstrates her friendship with him faking an SMS from Ramona, ignoring her own feelings towards him, in order to give Scott support in his fight against the two exes she also offers him her house (and her own bed) when Scott is homeless, helps him with his depression over Ramona's disappearance and even kisses him a last time before his fight with Gideon.
Captain America. Pretty much anyone can (and do, on many occasions) soliloquize about how much everyone adores the shit out of Cap, and never feel like they're laying it on too thick or being out of character; which is something that can't be done to many other characters without it tasting of a Creator's Pet. In the Marvel Cinematic Universe, being a Nice Guy is actually the only reason the Super Serum even worked - When it was given to a megalomaniac, it created the Red Skull. Colonel Badass Chester Phillips wanted to give it to a "Strong, Fast, Obedient Soldier, and sixty years later we get to see the results of THAT. Only a Good Man could become Captain America.
The squeaky clean Tintin is this, in contrast to the brash, drunken, and loud-mouthed Captain Haddock.
Mr. Tawky Tawny in the Shazam franchise sometimes causes a scare for being a humanoid tiger, anyone who takes the time to know about him will realize that he is a perfect gentleman and a wonderful person to know.
Major Mapleleaf from Alpha Flight, as befits a super-Mountie.
Jaime Reyes' Blue Beetle is basically Spider-Man without the world crapping on him as much. Thankfully, he has (or Had thanks to flashpoint) a strong supporting cast he could play off of.
And of Course, the Flash. No matter which one, The Flash will be this. Golden Age Jay Garrick, Silver Age Barry Allen, Bronze Age Wally West (though he bounced between this, Jerk with a Heart of Gold and Chivalrous Pervert), Dork Age Bart Allen, all of them are consistently great guys who can and will become the best friend and surrogate brother of anyone they're with.