WordPress offers a handy "Press This" bookmarklet that streamlines the process of writing a blog post about an article on another site. When reading something you'd like to link to, you click the bookmarklet, and a New Post window opens up with the title filled and a link in the body. If you select text on the page before clicking the bookmarklet, the selected text will be included in a blockquote in the body.
Similar functionality can be achieved with the Prepopulate module alone. QuickPost Bookmarklet adds an admin frontend to this that allows you to customize how your bookmarklet will work.