Here's a updated list of new ongoing ctf challenges. Feel free for adding some sites!
- Root Me (Root-Me is a non-profit organization which goal is to promote the spread of knowledge related to hacking and information security)
 - Pwnerrank
 - Over The Wire
 - WeChall
 - Smash The Stack
 - HachTheBox
 - PicoCTF (A CTF for middle and high school students)
 - CTFlearn (user-contributed challenges)
 - Hacking-lab
 - Enigma-Group
 
WebApp Specific:
Pwn Specific:
- pwnable.kr (all about pwning)
 - pwnable.tw (new site for pwnable challenges)
 
Reverse Engineering Specific: