When looking for economics books, it helps to know exactly what your specific goals are. The original poster was looking to understand economics, and to also be able to pass some tests.
For a beginner seeking to understand economics, I recommend Carl Menger's Principles of Economics. Look also at Richard Salsman's recommendations in his area for fundamental texts.
For a textbook that will help one pass a test on Micro & Macroeconomics, I haven't looked at them all, but "Economics: Private and Public Choice" by Gwartney and Stroup was better than a number of alternatives I've seen (I encountered it in my CFA study program), though far from perfect. To pass a standard test on economics, sadly, one must become quite familiar with the mechanics of some very false theories.
(See the following essay as a worst-case example:
http://www.capmag.com/article.asp?ID=1452)Beware of reading just books of polemics, if your goal is to do something practical with your understanding of economics. Unfortunately, it seems that the majority of "free-market" books on economics are primarily polemical - why Keynesianism is wrong, why Socialism is wrong, etc. I see far fewer books that provide positive insight into how an economist should approach economics.
In my work in investment research, I'm trying to identify specific relationships between various prices and economic factors to revenues and profitability of various industries, as well as investor reaction to these items. Mises' bias against mathematics to some degree stunted my interest in quantitative methods in economics early in my studies, but I've tried to recover from this. I don't know many modern Austrians interested in or able to tackle real-life short to medium term analyses like this.
In my view, there is a gaping hole in the economics literature. I wish I could see a pro-capitalist texbook which builds upon Menger's and Ayn Rand's foundations to develop a new theory of macroeconomics that attempts to at least some degree codify and quantify how the productive process of people and firms aggregate to create economic progress, and explain how various influences, innovations, negative surprises, external impacts, and government distortions can create changes in the economy. This would be a VERY useful book.
Unfortunately, I haven't seen much come close to this ideal. I have seen some presentations from Richard Salsman that were in the same vein, but a text like this would require 800 pages or so, and would require a huge amount of integration. Econometrics may provide some industry studies, but tends to be full of floating abstractions. Mainstream macroeconomics is terrible, but even the better macroeconomics perspectives are hobbled by a lack of a good and specific base.
Because I think economics can be better understood as being driven by the process of profitable production, I'd recommend that budding economists also study finance and investments. That field is full of errors too, but one must understand concepts like how firms perform capital budgeting and estimate the present value of projects over their estimated lives to really understand the underpinnings of economic progress and economic mistakes on a more concretized level. I would recommend the CFA self-study program as something worthwhile to budding economists, because it includes economics as one part of an integrated study of financial markets. (See www.cfainstitute.org.)