[masraum]

I haven't tried the Spanish version, but Pimsleur is an audio only course, and seems to generally be in top 2 of the most common "what's the best course" lists. Usually Pimsleur and Rosetta are mentioned as the top 2. Rosetta is a computer based thing, so wouldn't really work. Pimsleur is essentially all audio that you get by listening and repeating what you hear.

The Pimsleur course comes in 30 minute "lessons" that start slow and build on the last lesson. So at 30 minutes, they may be a great length for a commute.

I put some lessons on my ipod once to listen to in the car. I found that I couldn't pay enough attention while driving to really get the most out of them.