I second Schiff's "How an economy grows and why it crashes". It's kinda written as a fable/parable (think "animal farm"), but covers all the basics. A quick fun read that you could leave in your bathroom and read in a few sittings.
Another good 101 primer is Tom Woods' "Meltdown". While this is ostensibly a book about the recent crises from an austrian perspective, he does dedicate a few chapters in it to just covering the basics of the austrian theory in general.
And honestly, Human Action is very readable, just long. If you buy Murphy's study guide to help you along the way, you can make decent progress with it.
Lastly, depending on how philosophically minded you are, Hoppe's short "Economic Science and the Austrian Method" elaborats on the philosophical basis for praxeology (basically just elaborates on mises starting point, that it's impossible to deny that humans act).
Note: I downvoted the Hazlett and Hayek suggestion for two reasons:
1) Hazlett's "Economics in One Lesson", while a great read, isn't specific to the Austrian Theory. It could be equally applicable to any other free market school (eg: Chicago). It's a great read and basically just a rehash of Bastiat's 'seen and unseen', but not Austrian per se. (to put it another way, understanding Hazlet/Bastiat is necessary for understanding Praxeology, but not sufficient.
2) Hayek was trash; he was a state apologist at best. Contradicted himself frequently, non-praxological approach to the subject. Also a very boring writer.
Elaboration on why Mises > hayek, if you're interested: http://mises.org/daily/5747/
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