I thought some of you out there might be interested: there's a brand new Cepstral voice available. She's called Callie, and she's their best voice so far. Maybe she doesn't have quite the volume or dynamics of some AT&T or RealSpeak voices, but she's definitely got charm.
You can pick up Callie (that doesn't sound right, does it?) from TextAloud for $30USD. You can first download and try out her voice in TextAloud, although she'll nag you to register her. (By the way, you register her via Cepstral's SwiftTalker program, which installs with the voice.)