The HD3300 should already work with modesetting on the open-source drivers on either the radeon or radeonhd drivers. 2d/3d acceleration is being worked on and should be ready for end-users in the next few months.
There really isn't any discrete graphics card being sold today that is fully supported by open-source drivers, only Intel has open-source support for their most recent products. ATI is still catching up, and NVIDIA doesn't have a supported open-source effort at all (the Nouveau folks are trying to reverse-engineer NVIDIA cards, but that's tough going)
If you don't need open-source drivers. NVIDIA and ATI both have supported proprietary drivers.