No. 5: Superboy & Robin

Credit: DC Comics
The sidekicks to two of the most highly regarded superheroes in the DC Universe have a huge shadow cast upon them by their mentors, but that hasn't stopped them from making a name for themselves. The two have become vastly different than their mentors (which makes their characters that much more interesting) with Robin more lighthearted and Superboy less confident. Though Superboy has been depicted as being friends with both Dick Grayson (the first Robin and then Nightwing) and Tim Drake (now Red Robin and leader of the new Teen Titans), it seems that his relationship with Drake is the most bromantic.
Just like their mentors (who are also on this list) Superboy and Robin (Drake) met after joining a team, only this one was the Teen Titans. Along with their group, they became very close, living together and learning to become better heroes. As a team they found out that Superboy's DNA is only 50% Kyrptonian and the other half was human. Later they would find out that the human DNA in Superboy was that of Lex Luthor, Superman's greatest foe. Trusting him with his darkest and most dreaded secret, Superboy let's Robin know of his bloodline. Whether or not Robin already knew is up for debate, because let's be honest, Tim Drake is already as good of a detective as Batman (he figured out Batman was Bruce Wayne when he was barely a teenager).
With that secret as a bond, the bromance between the two grows even stronger, and throughout comic book history it seems that Robin and Superboy always seem to be the best of friends.