Get Featured Image Source

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<?php
$imgsrc = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), "Full");
echo $imgsrc[0];
?>

Instructions:

Using the WordPress Function wp_get_attachment_image_src, you can get the src of the featured image quite easily like this.

Related links:

http://codex.wordpress.org/Function_Reference/wp_get_attachment_image_src
http://codex.wordpress.org/Function_Reference/get_post_thumbnail_id