Rosetta Stone is a great piece of software. Particularly their online subscription service, which means that you don't have to buy the whole package, you can just try it out for a month or two before committing further. You do have to be connected to the Internet to use it, but in this day and age, that's becoming less of a concern.
One note of caution: Rosetta Stone use a fairly interesting teaching technique. Basically, they don't use English at all. Just pictures and the language you're trying to learn. Their theory is that what they are doing is mirroring how you learn language naturally, which makes a lot of sense. The trouble is, if you're used to learning languages in a more traditional way, with a focus on grammar, as well as vocabulary, it can take a little getting used to. But once you wrap your head around their method, you can pick up a lot in a very small space of time.