I highly recommend Debt: the first 5000 years https://www.amazon.com/Debt-Updated-Expanded-First-Years/dp/...

and Heilbroner's Worldly Philosophers https://www.amazon.com/Worldly-Philosophers-Economic-Thinker...

The Worldly Philosophers is my favorite. It will take you through economic history as told by its great philosophers and break down the differences between the schools of thought. It has been my trusted guide on economic theory for the last 15 years.

Here's a link on Amazon: http://www.amazon.com/The-Worldly-Philosophers-Economic-Thin...

Along with the excellent recommendations here, I would add "The Worldly Philosophers" by Heilbroner (http://www.amazon.com/Worldly-Philosophers-Lives-Economic-Th...) for a slightly different angle. It covers a wide range of famous economists and describes the high points of their theories along with some biographical detail, in a very engaging style. It's the economics version of "Men Of Mathematics", which is also a fascinating book.

These two are my favorite (that are reasonably priced!). Samuelson is definitely a formidable thinker and lays the groundwork for much later economic thinking.

http://www.amazon.com/Worldly-Philosophers-Lives-Economic-Th... http://www.amazon.com/Price-Theory-Milton-Friedman/dp/020206...

However if you go with the Samuelson, Fridman, and Heilbroner you'll be missing out on some key concepts relating to information and games, which are essential for understanding modern developments in economics.

So, I would also look at Myerson's Game Theory http://www.amazon.com/Game-Theory-Analysis-Roger-Myerson/dp/...

Finally, the empirical side of economics is quite important, and it is essential for investigating whether the theoretical conceptions (say in Samuelson) actually hold up. There are many bad texts, and the seminal ones (Greene) are quite difficult in the beginning. So, I recommend a pedagogical text that uses the likelihood approach. Although, this is, by no means, a comprehensive text, you can certainly gain an understanding of a basic econometric study http://www.amazon.co.uk/Econometric-Modeling-David-Hendry-Ni...

That should give you a broad introduction. Also, checkout http://papers.ssrn.com/sol3/DisplayJournalBrowse.cfm, which is an excellent resource with many free papers.

Good Luck!