Guides by Lonely Planet - Explore city guides curated by experts.
Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Pretty Streets - Discover cities through customized walking itineraries
Fetchee - Fetchee is a free price tracking wish list app that works with all online stores worldwide.
Foursquare 10 - Your ultimate city guide, in your pocket
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.