@ raybe,
You should check out a company called Cereproc for some more "worldly" voices. They sound quite authentic for their respective regions (Irish, Polish, Scottish, etc.). They are reasonably priced and the one I purchased works very well with UltraHal & Win 7 64.
Acapela and Loquendo are really great voices as well but I know one of these does not or will not work with Hal. I can't recall which at the moment but be sure to read the specifications first.
There is also
www.Ivona.com for a really nice selection of voices and I found a new (to me) site today called: Linguatec @
www.linguatec.netHope these give you something to crow about!

UPDATE:
Acapela has several really nice TTS voices that work with TextAloud but NOT with other TTS enabled programs like UltraHal UNLESS you
purchase the Infovox Desktop. It comes with a language group and includes the Heather voice that everyone seems to like. It will cost you about $190.00 USD and will work on ANY TTS based program including UltraHal!! Now...just reach a little deeper into those pockets!!