Google Base is a place where users can easily submit all types of online and offline content, which will be made searchable on Google. You can describe any item you post with attributes, which will help people find it when they do related searches. Google Base is is free and is currently available with English and German interfaces. Iinformations about all types of online and offline content are submitted to Google Base via a data feed or Google Base API.
Google Merchant Center is another way to manage Product-type items. It’s a new service that makes it easy to upload and manage the Product listings you want to appear in Google Product Search, AdWords, and other Google properties.
Compared to Google Base, the Google Merchant Center provides a better, optimized experience specifically for merchants. Google will continue adding features and improving the tools for uploading and managing product listings. Accounts using Google Base for Product listings have already been transferred to the Merchant Center.
The Google Product Search application is currently still in a beta version.