Here are some options for voices you can use to create your Spanish vocab podcasts with Vocabularium.
At present, the only supported option on non-Windows systems are the Cepstral voices. You can use the free demonstation versions of these voices, provided you don't mind the nag message that will appear at the beginning of the podcast. To remove the message, the full versions cost USD 29.99 each (unfortunately, you'll need an English and a Spanish voice!).
If you have or know of other voices for non-Windows systems that you would like to see supported, please send an e-mail with details to the feedback address given at the bottom of this page.
On Windows systems, you can in principle use any SAPI 5 compliant voice, although you should check that the voice in question works on your particular system. Some options for the English and Spanish voices include:
Cepstral currently publishes two Latin American Spanish voices and a variety of English voices. As mentioned above, the licensed versions cost USD 29.99 each. You can start with the free demonstration versions, which will insert a nag message at the beginning of the podcast, but which are otherwise fully functioning.
To get rid of the nag messages, a good price compromise for Vista users could be to use the free Microsoft Anna voice for the English parts of the podcasts, and to buy one of the Cepstral Spanish voices (currently USD 29.99).
The AT&T Natural Voices series includes two Spanish voices, currently priced at USD 35 each.
A free option for the English voice (if not the best) is to use one of the free voices supplied with Windows XP and Vista. Of these, Microsoft Anna, which comes with Vista, is tolerable available only on Vista at present.
If you don't already have them, you can download the Microsoft voices for free: the file you need is the one called SpeechSDK51.exe, which you then run.
Buying the Spanish version of Acapela Infovox will give you both an English and a Spanish voice for USD 190. The voices are comparatively expensive, but excellent quality. An unencumbered 30-day demo of these voices is available for download from the aforementioned link. Note that you need the Infovox Desktop version of the voices; some other Acapela voices are sold cheaply, but they are designed for specific software and are not SAPI compliant. Acapela offers Spanish voices with a peninsular accent.
Note: these voices do not currently work (at least with Vocabularium) under Windows Vista.
Do you know of a better English or Spanish voice than the ones listed here? (By "better", that could be in raw quality, or in quality/price tradeoff.) Or in any case, is there another voice you'd like to see supported? Let us know at email@example.com, remembering to take out the nospamz of course.