Some web sites show different content depending on the referrer. News sites like the New York Times, which display many of the articles only if you are a subscriber, make an exception if visitors click on results from Google and other popular search engines.
Google has a feature called "first click free" for sites that require subscription. "First Click Free is designed to protect your content while allowing you to include it Google's search index. To implement First Click Free, you must allow all users who find your page through Google search to see the full text of the document that the user found in Google's search results and that Google's crawler found on the web without requiring them to register or subscribe to see that content. The user's first click to your content is free and does not require logging in."
While the first click is free, when you click on a link from the page, it's likely that the site will ask you to register. This is especially annoying for sites like nytimes.com, which use article pagination to increase the number of page views.
One workaround is to copy the URL of the page you can't access directly in Google's search box and click on the first result. If Google didn't index the page, you can use SearchWiki to add the page in the list of search results: make sure you are logged in using your Google account and click on "Add a result" at the bottom of Google's search results page.
Another option would be to use the credentials collected by BugMeNot.