Wordpress - Get the blog page URL set in Options

To build on Sagive's answer, you'll want to wrap the ID in get_permalink() to get the actual link.

<a href="<?php echo get_permalink( get_option( 'page_for_posts' ) ); ?>">Our Blog</a>

As of WordPress 4.5 you can use:

get_post_type_archive_link( 'post' );

This handles the logic of getting the correct URL regardless of whether posts show up on the homepage or in a specified page.

Best way to check the option before setting the permalink is as follows:

if ( get_option( 'page_for_posts' ) ) {
   echo '<a href="'.esc_url(get_permalink( get_option( 'page_for_posts' ) )).'">'.esc_html__( 'Blog', 'textdomain' ).'</a>';
} else {
   echo '<a href="'.esc_url( home_url( '/' ) ).'">'.esc_html__( 'Blog', 'textdomain' ).'</a>';
}