Assimil is the best program I've found so far for learning a foreign language. The way you learn the language feels very natural to me. I used their book but they've recently released an app which may be good.

I also recommend Pimsleur as a supplement to work on your accent and listening skills. Don't let the limited vocabulary misguide you...Pimsleur teaches and emphasizes a lot of very useful language patterns/structures. Great tool in the language learning toolbox