Multiplicities of Discriminants - http://www.algebra.at/multi.htm Formulae and tables for the number of non isomorphic fields with a fixed signature and Galois group sharing a common discriminant.
Discriminant Exponent Calculator - http://www.public.asu.edu/~jjones/java/discrimexpo.html Java applet computing the maximum exponent of a prime in the discriminant of a number field of given degree.
Algebraic Number Theory - http://www.numbertheory.org/courses/MP473/ A course by Keith Matthews. Lecture notes (GIF slides), bibliography, web resources.