The free Xfrog plants that are available on their site as samples are pretty good. Limited selection, but each pack has three plant variations. They are available in .vob format: http://xfrog.com/category/samples.html

For Vue native plants, I can recommend The "Incredibly Lush" series plants (C3D), the plant packs from Realms Art (also C3D) as well as the plants from AsileFX.

Ciao

TD