A lot of really great work is happening in academia; I'm not going to name names because I'd forget someone deserving.
(Shameless plug: we [0] do speech and language consulting including custom TTS.)
[0] cobaltspeech.com
Also, I'm really linking to research groups, so take these names as starting points and look at their students and other professors working with them.
First off, the Blizzard challenge is a major hub of activity. [4] Festival is an important piece of software [5]. Interspeech is an important conference [6] (take a look at the speech synthesis track and the organizers for that).
Alan Black [0] @ CMU is kinda a giant.
Keiichi Tokuda [3] @ Nagoya also a giant.
Simon King [1] @ Edinburgh, just had a paper linked to on HN a few days ago and does important work.
Mark Gales [2] @ Cambridge does work here, too.
[0] https://www.cs.cmu.edu/~awb/ [1] http://www.cstr.ed.ac.uk/ssi/people/simonk.html [2] http://mi.eng.cam.ac.uk/~mjfg/ [3] http://www.sp.nitech.ac.jp/~tokuda/ [4] http://festvox.org/blizzard/ [5] http://www.cstr.ed.ac.uk/projects/festival/ [6] http://interspeech2015.org/wp-content/uploads/direct/INTERSP...