Deadpool the Terminator (Deadpool + Deathstroke). Would have mixed the names up more, but "Deadstroke" and "Deathpool" sounded really awful, even by Amalgam standards. Imagine Deadpool scheming to destroy a group of teen sidekicks, running around with his teenage assassin children, and insisting that everyone wear eyepatches. It practically writes itself.
Spider-Boy (Spider-Man + Superboy). I know that Amalgam already took two swings at this one, but they missed a big opportunity given that the earlier mash-ups took place around the same time as the 1990s Clone Saga. It's Ben Reilly by way of Connor Kent--the teenage clone trying to live up to the ideal of the original, but challenged by the fact that half of his cloned DNA came from evil mastermind Norman Luthor.
The Sensational Wonder Woman (Wonder Woman + She Hulk). She's a green-skinned Amazon lawyer-princess. Good luck trying to lie on the stand when the prosecutor has the golden lasso. Also, an excellent opportunity for bad legal puns as battle banter.
The Bat-Man: Man Without Fear (Batman + Daredevil). Considered a Batman / Iron Man mash-up, and while that would also be awesome, look at the similarities here. Batman and Daredevil are both darker characters focusing on street-level crime with backgrounds in martial arts. Industrial heir Bruce Murdoch lost his sight in the factory accident that claimed the lives of his parents. He gains no superpowers, and is simply blinded. Suspecting foul play but unable to prove anything, young Bruce travels the world, and basically becomes Batman. In a stunning feat of medical engineering prep time, he designs a gadget that uses sound to create a crude visual image that feeds into his brain. He then follows the chain of corruption that led to his parents' deaths and his blindness to a competitor of Murdoch Enterprises--Ace Chemical, and its millionaire "philanthropist" head Wilson Kerr. For the costume, the Batman-Daredevil blend would probably look something like the Batman Beyond costume with an open chin and short ears (no cape, but probably small gliding wings), and his weapon of choice would be Daredevil's billy club.