USPTO's Online service provides a central location where you can search, file, pay, and obtain status for patents and trademarks.
Using PATENTSCOPE you can search patent documents including published international patent applications.
Worldwide "Patent Searching" provides simple listings of quick links to all the patent databases on the Internet. If you want to do a search, you only need go to one page, and select the database and entry point you want with a single click. Help and information are provided. However, most of the patent search databases are fairly easy to use.