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:

• Pentesterlab

Pwn Specific:

• pwnable.kr (all about pwning)
• pwnable.tw (new site for pwnable challenges)

Reverse Engineering Specific:

• Microcorruption
• Reversing.kr

• Damn Vulnerable Web Application - DVWA
• Web Application Exploits and Defenses
• Exploit Exercise
• WebGoat