Recommended and mentioned products
"When the price is right, you will play all night."
You'll see sales of games from authorised Steam key distributors, such as Steam themselves, Fanatical, Humble, Green Man Gaming and many more on isthereanydeal.com knowing you're getting a good price and supporting the developer.
Very good and clear site for best deals.
Enhanced Steam fork by IsThereAnyDeal.
I recommend the Augmented steam plugin: https://augmentedsteam.com/.