You have several options:
1. Login to phpMyAdmin, and manually change the "siteurl" and "home" records in the wp_options table.
2. Open up wp-config.php, and add these lines:
define('WP_HOME','http://your.correct.url.com/path/to/wordpress');
define('WP_SITEURL','http://your.correct.url.com/path/to/wordpress');
Then you may access your site. Go to admin, change back the site url on the admin page as well, then remove the above lines from your wp-config.php.
For more options, see: http://codex.wordpress.org/Changing_The_Site_URL