Thieve - A curated list of the best products on AliExpress
Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Friendshop - Get deals on the best in beauty when you shop with friends
Fetchee - Fetchee is a free price tracking wish list app that works with all online stores worldwide.
monote - Easily remember and organize products you want to buy
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.