Here are some websites that provide in-depth stats and insights into champions, items, runes, and counters in League of Legends.

OP.GG

• Champ Stats / Leader Board / Tier List / User Search Tool / Aram Tier List

U.GG

• Champ Stats / Leader Board / Tier List / User Search Tool / Pro Builds / Aram Tier List

Leagueofgraphs

• Advanced Stats / Leader Board / User Search Tool / Replays

Porofessor.gg

• Live Game Stats

Deeplol.gg

• Champ Stats / Leader Board / User Search Tool / Aram Tier List

Blitz.gg

• Champ Stats / Leader Board / Tier List / User Search Tool / Pro Builds / Aram Tier List

Mobalytics.gg

• Champ Stats / Tier List / User Search Tool

Lolalytics

• Advanced Stats / Tier List / Leader Board / User Search Tool / Aram Tier List

Counterstats

• Counter Pick Stats

lolvvv

• Pro Player Stats / Pro Builds / Pro Player Search

METAsrc

• Stats / Tier List

ChampionMastery.GG

• Champion Mastery Leaderboard

LOLTheory.gg

• Champ Stats / Patch Comparison

rewind.lol

• View your stats from the past

KoreanBuilds.net

• Strategies, builds, and runes directly from Korea's diamond, master, and grandmaster players.

EuropeanBuilds.net

• Strategies, builds, and runes directly from Europe's diamond, master, and grandmaster players.

fow.lol

• Champ Stats / Leader Board / User Search Tool