SellerCloud - SellerCloud is a multi-channel inventory and order management system.
Camelcamelcamel - Easily monitor Amazon product prices and get alerts when they drop.
Sellbrite - Multichannel ecommerce management for serious sellers.
Fetchee - Fetchee is a free price tracking wish list app that works with all online stores worldwide.
ecomdash - An easy-to-use inventory management software enabling small business to automatically sync inventory across sales channels - from one centralized software (SaaS).
Keepa - Price history charts and the option to be alerted on price drops for all Amazon sites.