There're many places to search for individual patents -- the US Patent and Trademark Office and Google Patent Search are two examples. But sometimes that's not enough. If you're trying to identify trends in innovation over time or analyze all the patents relevant to your invention, it helps to have all the patent data on hand.
"Google and USPTO have entered into an agreement to make the following USPTO products available to public at no charge: Patents (grants, applications, assignments, classification information, and maintenance fee events), Trademarks (grants, applications, assignments, and TTAB proceedings). All data originated from USPTO -- with both full text and images. Google is hosting this data unchanged, except for repackaging into zip files. And in the future we'll be making more data available including file histories and related data," noted Google.
More Info: USPTO