Rather than repeat what everyone else has been saying, I'll let some books do the talking for me... (Should be available from any good book store online or at your local book store)

Bruce Schriner - Applied Cryptology, Second Edition Best cryptology book I've seen... discusses algorithims and security in general... ($60)

Hacking Exposed 2 - (Insert authors here) Huge section on what not to do... ($40)

Good luck
Zak