"computer voice" software?

I need a highish quality program (read: it sounds good) that can generate a computerized voice.  It can be text-to-speech (I type, it talks) or it could even be something that takes my own voice and modifies it (a-la GLaDOS in Portal).  Anything that will mask my voice and turn it into something electronic.  I already tried one (it was just called "Text2Speech") and it kind of sucked.  I'd like something that actually sounds good.

And no, I'm not plotting anything illegal.  I'm making a video for school and I want the effect.

>>9

yah that was cool.  tell meeee plz