I took Princeton Review's online course and wholeheartedly recommend them, either classroom or online (I had access to the instructors through the online chat and they were awesome). The practice drills were excellent (the online drills are tailored to your performance) and the materials in general were really solid. It comes with the Official Guide. When I was researching courses a few months ago, Kaplan didn't even tell students about the OG, which is insane. Official materials are a must (including GMATPrep). I don't know if that's still the case, but either way I would recommend PR over Kaplan.

I disagree with the Kaplan 'insanity' comment. I used only a $20 Kaplan book and the Powerprep software, and scored very well on the test. It's more important to think about your process for each question than to do 1,000+ practice questions.

OG's question banks are good, but many of their methods are absolute garbage. I've tutored GMAT for 5+ years with several of the big companies and have seen all of the major materials.

My advice is that Kaplan is the best place to start *unless* you are already quite strong and are looking to add 50 points to a 700 or so score. If that is the case, some of the other materials out there are more thorough and advanced. The problem is that this can be overwhelming to a student starting in the 500s, and little or no improvement is often the result.