(A bit of a vent tut. whilst redrawing the huuuuge Avengers promo art in pony form...blarp.... )
Here's a quick little doodad I cooked up for you that might help all you aspiring animating bronies out there, a chart that features basic pony mouth syllables and phenomes.
It's pretty slapdash to me, if I had enough time I would've fully inked the heads but I think this will suffice. If you need any help with how to make sounds that aren't on there, just go ahead and comment!
No offense, but these seem to only fit mares, a stallion mouth is a bit more blocky as you may know. if you could do one for stallions, that would be great.