Duolingo is great for the start I think... it is nothing for "learning" a language well, but it gives you a really good idea about it and is also nice in order to review grammar topics. Moreover, there exist tons of softwares- and internetsites. Many friends of mine love babbel (I haven't tested it yet). Furthermore, you could check groupon regularely. They often have offers for learning a language online.
But I think that softwares and learning alone won't make you fluent in any language. You need to attend at least some classes or look for intercambios in the internet. I have learned tons of grammar and vocabulary, but I absolutely lacked in conversation skills. Thus, I went to Spain and learned at a language school, where I improved a lot- a Spanish immersion is always the best way to go. Ailola, my language school in Madrid, offered high quality lessons for a reasonable price. The course was demanding and thus, I learned a lot, although it was a bit exhausting at times. If you ever have the opportunity to go to Spain I can absolutely recommend Madrid. It's an international city and people are simply lovely