We used Muzzy Spanish and German, and it was great for the toddler/pre-school years. We checked out Rosetta Stone but my DD12 didn't like it much, so now we are doing LiveMocha. I really like this program- even preschoolers can use it (though they might not be ready for the writing portion, which is okay). One of my favorite things about LiveMocha is that its free.
DD12 is learning Japanese this year, and we have found some other resources for that language. One of her favorites is Genki Japan- they have lots of cute and engaging videos on YouTube.
Some other great ways to introduce foreign language is with music- we listen to a lot of popular German music as well as Disney songs in German. We have done this with Spanish also.
