When it comes to having a good sound, what you really want to look for is not the text to speech software, but the good voices: they are a separate subject.
The same voice will work accross different software. The best one I know of at the moment is named Audrey. A female voice with a british accent. Although I have to change most ' that are on the text with copy-past to one from the keyboard, it is worth it for an almost realistic sounding voice. I also have to place a pausing symbol (.,: or such) at the end of titles so she doesn't keep talking right through them. I still think it's the best voice I have so far. But I wouldn't mind finding the one from that weather channel that was mentioned ealier:
"NOAA weather radio broadcasts are EXCELLENT. I would not object to listening to that program read a long text.– Jeanne Pindar"
Here is a website which has sample voices on it: including Audrey. I have others, but I have only used her for a long time now.
PS: you have to pay for the better voices, but they will work on free text-to-speech software afterwards... at least the one I have. (Free Natural Reader)
Voice Sample web page: