The Pixel 4 is, on balance, my favorite phone Google has ever made. It's wonderfully compact, it has a good telephoto camera, and I'm a big fan of secure face unlock. It launched at $800 in 2019, which plenty of folks thought was steep for what the little guy offers. If you're in that camp but have always wanted to try one, now's a great time: it's down to $400 on Amazon.
Now, this probably isn't a great deal if you're looking for a new daily driver: the Pixel 4's battery is unequivocally bad and it's coming up on its software support end date as soon as October of 2022. But it's also getting Android 12 and 13 (and should be eligible for the latter's beta program), so if you're a developer or just a passionate Android geek and want to stay on top of the latest developments for the next year and change, it's certainly an option.
The discount is available on Amazon and B&H. Stock is running low (at least at the former), so if you're into this, you probably shouldn't wait.