Skyscanner - Skyscanner.com compares over 1000 airlines to find you the cheapest airfares, fast.
Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
KAYAK - KAYAK is a travel search engine that searches hundreds of other travel sites at once. Our helpful tools & features find you the information you need to make the right decisions on flights, hotels, rental cars and vacation packages.
Fetchee - Fetchee is a free price tracking wish list app that works with all online stores worldwide.
DealExtreme - Online shopping for cool gadgets at the right price.
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.