The Pimsleur stuff is pretty big. It is broken up into three courses, I, II and III and each one contains 30 units that are about 45 min-1 hour. I've been doing the French ones, in addition to taking courses at school, for over a year and I'm about 2/3 through course II. I do some units more than once, though, and sometimes I'll get tired of it and go a month without listening to them. I think they're great, though. Really high quality stuff. It took 15 CDs to put just the course I of the Spanish set on disc for a girlfriend a few months ago.
FWIW I feel like I've benefitted a lot, especially in my conversation skills and accent, from the French discs.