Two logic textbooks by Smith (Intro Formal Logic, Intro Goedel's Thm) free for download

Corrected versions of the second editions of
  - Peter Smith, An Introduction to Formal Logic
  - Peter Smith, An Introduction to Goedel's Theorem
(originally published by CUP) have been made available as free PDF downloads by the author.

The first is an introduction originally based on the Cambridge first year course for philosophers. The second, although published in a philosophy series too, could be of more interest to mathematicians as it is more maths than philosophical commentary.