Although there hasn't been a cross over between Superman and the Turtles yet. We can only hope. After all Supes did teamup with the Thundercats why not the Turtles.

Batman
Blade
Captain America 
Catwoman
Daredevil
Elektra
Fantastic Four
Green Hornet
Green Lantern
Incredible Hulk
Incredibles
Punisher
Robocop
Shazam
Spiderman
Steel
Supergirl
Swamp Thing
Teen Titans
Teenage Mutant Ninja Turtles
Wolverine
Wonder Woman 
X-men