I’ve prepared a list of all Important coding contests, might be useful for you guys.
ACM ICPC
Code jam
kickstart
hashcode
TopCoder Open
Facebook HackerCup
Yandex.Algorithm
VK CUP
Challenge 24
SnackDown
TCS codevita
Codegladiators
smart india hackathon
HackWithInfy
Tell me if I missed anything.
AtCoder Contests are the best and most important (with respect to improvement) contests according to me 
What I mentioned are those which are held yearly with onsite final round and are worth mentioning in your CV if you get a good rank, also they have great prizes for the toppers.
I am not sure if Atcoder does that, but their regular contests are good.
You should also mention some good regular contests which people should participate in apart from big contests which are held anually
also add the date and registration link of contests if you can…It will be very helpful…
Facebook HackerCup is going to be live today after 10:30 pm
it would be good if u can provide dates (expected) with contests