IVONA has some great voices: http://www.ivona.com/en/

Alas, all of their SaaS plans have the same price: "negotiable". I never felt like negotiating, so I have no idea if they're affordable; unfortunately custom pricing usually means it's not the case.

http://www.ivona.com/en/saas/offer/

Yes. This is what I absolutely hate - I will never 'ask for prices' because I know it involves a harass-y phone call in my future. Such a shame people aren't more open.

The robot I work with (http://wiki.ros.org/Robots/AMIGO) uses a proprietary stand-alone package from Philips which works really well. Somehow, our license expired and now we use Festival, which works, but I really miss its old voice. Especially for Dutch text-to-speech it works quite well.

But for the life of me I can't find a link of where you could buy it.

Doing TTS correctly, with intonation etc. is really hard. Its not really my field, but I can imagine that getting intonation right is near impossible with just unannotated text.

I figured as much. I've been using Festival myself, which seems OK. But there appear to be a million voices and I have no idea which ones are supposed to be the best.

I've found this to be one of the better ones http://www.ispeech.org

Yes, the Czech version only sounds like a person after a stroke...

acapela infovox have the best voices I've heard.

http://www.acapela-box.com/