Google has launched a patent search engine.
Google Patent Search now allows you to search the US Patent Office and will presumably expand in time to include other patent offices. Running a search is pretty easy but actually finding what you are looking for requires you to use pretty specific search terms to avoid a multitude of irrelevant search results. Fortunately the advanced search page gives you a number of options to help refine your search including patent number, title, assignee and dates the patent application was filed.
I ran a search for the iPhone and this result was the first one:
Google Patent Search apparently uses the same basic software as Google Book Search so you can browse the pages and zoom in on the illustrations.