Google has a new shopping API which splits into two components: Content and Search. With the introduction of the new API the Base API is being deprecated.
The Content API allows retailers to upload product details for use almost anywhere in Google that it makes sense - product search, ads, and so on. The Search API can be used, as its name suggests, to perform searches on the products uploaded using the Content API. What this means is that you can build applications which search across merchants for the best price or deal on a given product or type of product. The APIs are available via the Google APIs management console - Google API Console.
Google's replacement shopping API means the end of Google Base which was a broader attempt at providing access to structured data. Using it you could upload almost any kind of data, have Google host it and search it for you. If you built anything using Google Base you have until June 1 2011 to move it over to the new Shopping API - however you might not be able to as the new facility only supports shopping. What this means is that non-shopping applications, such as real estate, events, jobs, activities and other structured content, will have to find an alternative host. There is a guide to migrating to the new API - Migrating to the Content and Search APIs for Shopping
Content API for Shopping
Search API for Shopping.