Do a simple internet search for "learn ( language) for free" or "learn (language) online" and sift through for your best option. For Spanish and French there are interactive websites where you can communicate with native speakers and other learners of the same language.
Check university websites for learning resources and listen to podcasts in the language you want to learn. There are thousands of sites for learning foreign languages. Check the Resources below for a few I've found most helpful.
Find government programs and grants for critical langauges. As part of the National Security Language Initiative the federal government offers grants and scholarships for people interested in learning critical languages both in the US and through programs abroad. Their programs range from a month to a few years as a Fulbright Scholar. See Resources below.
Participate in a language exchange. One on one conversations with a native speaker of the language you're learning can be extremely beneficial. Offer your English (or any other) language skills in return for theirs. Generally, you meet up at a cafe or library once a week and spend half of the time teaching your language and the other half learning theirs. College campuses and message boards at work are the best ways to find exchanges but you can also ask friends and neighbors and do internet searches.