If you are not averse to voice synthesized speech, you may quickly edit the free notes people have posted out there, questions you find important, etc and make an audio-book yourself.
Especially if you make one with your own errors, rules you need to memorize, even formulas (rewritten as text) it may be of tremendous help.
It may not turn out to be one of the longest and most intriguing books you have ever read, may not make your commute pleasant (especially if you listen to the same stuff 10s of times), but will surely etch some concepts permanently in your mind.
It helped me a lot when I was studying for both my financial designations, despite the quant nature of much of the topics.
In short:
(1) Have a place (folder, file) to clip text to that you will be synthesizing (or even reading out loud if you have the time to waste and the material is short); start small - when you make your first 15 audio files by 4 mins -> put them on your player. You may want to make 400 audio files initially, but be modest, start small =)
(2) If you are not averse to Microsoft Sam - you have it for free in windows; If you want a better voice and are willing to pay - you may purchase the Neospeech Paul voice;
(3) You will need an efficient software (besides the voice). I really like Balabolka (free and downloadable from sites such as download.com) which is very versatile - I use it to split a big txt file into 3KB segments and then convert these to mp3 - the software does it automatically for you.
Well, you know one of my greatest secrets now =)
P.S.: On a side note - If you are not keen on doing the above, and do not have the time to read GMAT Fiction, you may go over to project Gutenberg and get some free classics, read by volunteers (or again - synthesized...)P.S. I may actually start a thread on the issue, it will be my first one =)