I'm a network security analyst. Either of these two books would be a good place to start. Also, if you are looking for a decent community for this type of thing, visit reddit.com/r/netsec.
This next site is basically Youtube for security conferences. They also offer some online courses on writing exploits in assembly and python, but not all of them are free.
Hacking: The Art of Exploitation, 2nd Edition
http://www.amazon.com/Hacking-The-Art-Exploitation-Edition/d...
Hacking Exposed 7
http://www.amazon.com/Hacking-Exposed-Network-Security-Solut...
This next site is basically Youtube for security conferences. They also offer some online courses on writing exploits in assembly and python, but not all of them are free.
http://www.securitytube.net/
Computer security is just like programming, you can obtain a world class education for free, from the Internet. You just have to know where to look.
I haven't read the books that the other guys mentioned, but I've seen them recommended so often that I'd bet they're worth a read as well.