Frege's Theorem
   Article in the Stanford Encylcopaedia of Philosophy, entitled `Frege's Logic, Theorem, and Foundations for Arithmetic'. Discusses the 1980 discovery of Crispin Wright that Frege's work of the Grundgesetze can be carried out in second-order logic with Hum
   http://plato.stanford.edu/entries/frege-logic/index.html

Logic
   An online textbook by Garth Kemerling, explaining the basic elements of elementary logic at an undergraduate level.
   http://www.philosophypages.com/lg/

Logic and Mathematics
   Essay on the nature of logic and its relationship to the philosophy of mathematics, written by Stephen G. Simpson.
   http://www.math.psu.edu/simpson/papers/philmath/

Nordic Journal of Philosophical Logic (NJPL)
   Edited at Dep. of Philosophy, Univ. of Oslo, published by Scandinavian U.P. in hard copy and on WWW. Full-text Web edition free for personal use.
   http://www.hf.uio.no/filosofi/njpl/

PHILOG
   The Danish Network for Philosophical Logic and its Applications.
   http://www.philog.ruc.dk/

Peirce's Logic
   Article in the Stanford Encyclopaedia of Philosophy, by Eric Hammer.
   http://plato.stanford.edu/entries/peirce-logic/

Philosophical Logic
   Introductory article by E. J. Loewe.
   http://www.dur.ac.uk/~dfl0www/modules/logic/PHILLOG.HTM

Symbolic Logic
   Online resources provided to supplement undergraduate course taught by Peter Suber. Good collection of handouts.
   http://www.earlham.edu/~peters/courses/log/loghome.htm

The Troublesome Paradox
   Online version of book seeking publication by Per Lundgren. Author attempts to argue that a consequence of Goedel's incompleteness theorem is that we should overturn our current approach to scientific method.
   http://www.yesgoyes.com/

Tips on Translating English into First-Order Logic
   An introductory guide by Peter Suber.
   http://www.earlham.edu/~peters/courses/log/transtip.htm

Why Aristotelian Logic does not Work
   An essay at Abelard.org outlining an argument against Aristotelian syllogistic. The argument focusses upon the relationship between Aristotle's categories and his conception of being, attacking them from an idealist position drawing upon Brouwerian intui
   http://www.abelard.org/category/category.htm