Isthereanydeals. Frequently see steam keys available for cheaper than it is on Steam.

Recommend using it as a resource before buying games since it tracks prices, so no need to spend more than necessary.

Example is recently released ARC Raiders where you can save a few bucks.

https://isthereanydeal.com/game/arc-raiders/info/

I've often wondered who is paying full price buying from Steam at launch over sometimes buying the same Steam game from another storefront for 10-20% less. Guess its people who think games aren't sold cheaper than on Steam.