
1) Smith's Introduction to Godel's Theorems http://www.logicmatters.net/igt/ is a great book, with all the mathematics but willing to go into the philosophy.
2) Franzen's Gödel's Theorem: An Incomplete Guide to Its Use and Abuse http://www.ams.org/notices/200703/rev-raatikainen.pdf is enlightening in a different way.
I'll also mention a favorite author around here http://www.scottaaronson.com/blog/?p=710 .
Hackers will be interested especially in the rather weak attempts to use Gödel to make all sorts of silly inferences about artificial intelligence and the nature of mind.
Probably no scientific result of the 20th centry, except maybe the theory of relativity, has been used by so many to prove so much while understanding so little.
"If T is effectively axiomatized, in the sense that there is an algorithm for deciding whether or not a given sentence is an axiom of T,..."
In Computability: Turing, Gödel, Church and Beyond Martin Davis even makes the definition "T is axiomatizable if it has an axiom set that is computable" on page 42.
And that's also the definition Shoenfield gives on page 125 of Mathematical Logic.
Besides, "effective" has always been a synonym for "computable", "recursive", or "decidable" whenever I've encountered it in this context.
Also, I must insist that "it makes no difference whether we require the axioms to be recursively enumerable, recursive, or primitive recursive." is not what Craig's Theorem says. This is dangerously close to claiming that recursively enumerable sets are recursive which is plainly untrue. If recursively enumerable axioms (not just recursively enumerable theorems) are indeed interchangeable with recursive axioms, then I'd like to hear more about that.