Today, Amazon is offering all the e-book versions of Kaplan test prep books for free. MCAT, LSAT, GRE, GMAT, Board Exams, Nursing, SAT, everything! Go to Amazon and search "Kaplan" in the Kindle store. You can use the E-book on a Mac or PC.
I use this site dailycheapreads.com, most of the time it is only fiction, but sometimes you get really good financial/biz books for free (or almost free).