IVONA speech engine is similar to SVOX but having used both, I think IVONA sounds better. Currently it is in beta and it can be had free from Google Play and the voices are also free.
The beta seems to work very well. Only bad thing is when downloading the voices it can take around 10min even on WiFi (guessing their server connections are not the greatest).
Not sure how long the beta will last so check it out while you can.