Scott's site is an obvious starting point for great Arsenal stats.

The current king of statistics sites is Fbref.

Statsbomb is a great general stats site with strong analysis and useful tools like radars.

Understat is a good starting point for all things xG.

Whoscored is a place to find the basics. Passing percentages, shots, tackles, touches. All the stuff we used to consider "stats." Now you need a PhD in mathematics to be a football supporter obviously.

Transfermarkt has information on player contracts and transfer market valuations.

Arseblog isn't just a great blog. His site has fantastic tactics articles and statistical breakdowns.