There have been cool resource sites available since League of Legends came out. However, there are many of them and it can take a while to find the best ones.
If you are looking for strategy/picking help there are several sites that help you during the picking/banning phase. Our personal favorite is LoLalytics where you can search for players and champions and see their popularity, ban-rate, win-rate and top win-rate by a single player (with some conditions).
At League of Graphs you can see the champions and their best counters. For example if you would like to play Zoe but are unsure how strong the champion is against your opponents picks and together with your teams picks. It’s easy to get these answers, just look up Zoe.
Okey, so you made some good decisions during picking phase, good! That gives you an edge but what about item builds? Don’t worry there are statistics programs to help you with that too. Our favorite is lolmath.net where you simply input the champions for the two teams as well as their positions. In addition to this you are given an stat preference meter where you can pick your preference on a Defense/Damage scale.
Porofessor.gg is a new site with live features which is great if you want to check if a friend is playing. Statisics are live recorded and you can see all kinds of data from position to rating to the players game history. There’s additional fun elements added to the ingame stats with different tags. You can see both good and bad “awards” that the players accumulate during the game. For example one player might get the “good warder” and “cold streak” award while another might have “Unkillable laner” and “Camille lover”.