That would be Granule. Check the Application Catalog at the Maemo Wiki.

It seems to me that the Granule site has links to sites with pre-built flash cards.

Also, I think Granule can pronounce words in the desktop version; hasn't been worked out how to do that on the 770. I'm thinking Flite, the Festival Lite TTS engine, might be able to be used here, but that's jumping ahead a few steps.