This is a very useful site. You enter any positive integer and it will return a prime factorization of that integer.
http://www.rsok.com/~jrm/factor.html
The Prime Pages; there is a lot here. Articles include the “Guinness book of” prime number records, how to find primes, conjectures and open problems, and some special types of primes:
http://www.utm.edu/research/primes/
This is a nice site, but is probably more than you want to know about primes:
http://mathforum.org/library/topics/prime_numbers/
Listen to the primes:
http://www.utm.edu/research/primes/programs/music/listen/
View the primes:
http://www.lactamme.polytechnique.fr/Mosaic/images/CONFORME.31.Fi.D/display.html
The largest known primes:
http://www.utm.edu/research/primes/largest.html
There is a lot of interesting material on the web concerning Goldbach’s conjecture. The follow site provides a numerical calculator.
http://www.matheasel.com/calculators/goldbach.html