Decent text-to-speech software for PDFs

I'm looking to listen to PDFs and e-books instead of reading them. Can anyone recommend some decent software that has a decent sounding voice? I have tried a few but most of them sound very robotic. I would be willing to spend a decent amount of money as long as it works well.

 

Dragon is the software used in a lot of schools.

 

Thanks, I use Dragon all of the time. It actually goes speech to text I am looking to go text-to-speech.

 

Opps, the other software they use in schools is Kurzweil.

 

Thanks, that name rings a bell but I never knew what it was for. I will give it a try

 

I visited a special education classroom last spring and those were the two programs they were using to help with literacy.