What's nice about Movieverse is that only Starscream mass-shifts to any extreme degree. Everyone who's in scale in one mode will still be in scale in the other.
I've got to update this, but:


Everyone here is around 1/60 scale; Deluxe Optimus Prime, Wreckage, and many Legends cars fit in it, too. It ranges from 1/low-50s to 1/high-60s in exact scale, which is admittedly a large gap, but it's as close as we're ever going to get. Besides, the only thing immediately "off" (besides the mass-shifting Starscream) are the tanks that should really be the same size.
No Ironhide or Ratchet fits here, unfortunately. Really need a Scout of those two.


1/90 Scale. Not much use for screen-accuracy, but a lot of the aircraft TFs are at this scale, including Skyhammer and Incinerator.


1/5 Scale is pretty much just limited to these two. And maybe FAB Frenzy (don't have him, so don't know exactly).
Definitely check out the Transformers Scale Project TulioDude linked to. A lot of effort went into that.