1. Exploit Writng :
I love this site. A lot of information and tutorials. If you are interest to write exploits then go to corelan. There are currently 11 exploit writing tutorial which is basic to advance and even better than others commercial course .
Thanks peter (respect)
2. Vulnerability Research:
If you are serious then you need these site. We always need to search new/old vulnerability. So these site are very good for starting:
Metasploit is popular framework for pentesting. Metasploit is very useful for quick shellcoding .