I'm a French teacher, and I think Rosetta Stone is fine, though ideally you'd want to supplement it with some human interaction, particularly if you're looking to become proficient.
Bmore, have you considered taking some online lessons? I offer them, and I know that other teachers/services do as well. Often, you can arrange to take a lesson here and a lesson there to supplement your other studies, rather than signing up for a complete course. PM me if you want more details.