There’s a good one for Amazon called Keepa that shows you the price history of the item. Helps a ton keeping prices in check during sales like Prime Day to see how much you are actually saving, if anything.

Also nice to see how much you could potentially save if you just wait for the next sale or if there was already a price decrease. Often times it looks like I’m good buying without waiting for any sale as the sales only knocked off a few dollars, at most.