Understand. Didn't mean to sound flippant. The sphere of 3rd-party app-providers for FCPX is growing... but it's still small enough that most of us are familiar with most of their products. The main ones are: (in no particular order)
OTHERS: (minor, IMHO)
Perhaps knowing these names will help your search!
Is there a 3d plugin that would import 3d files into FCP X?
afaik, just one:
the demoes are nice, but you very soon stumble into the main problem with 3D:
a 3D-title is a seperate 'layer' with its own physics, aka lights, material etc.
but… , when I like to add a simple Flying Saucer to my son's movie, I instantly run into trouble, if I want to make it look real, or at last 'integrated': position of sun, perspective, camera movements etc etc etc .....
... I guess, hobbyists like me have to wait another 10y for making my own Transformer movie