[Plugin: Link to Post] Does the job

Does what it says. Doesn’t do any fancy shortcode magic to keep links valid if your permalink structure changes, which I kind of expected; just hard-codes the URL into your post/page. It’s a modal box with a search feature, which is handy. But personally I don’t think it warrants a plugin just to help you find the URLs of posts/pages on your site.

http://wordpress.org/extend/plugins/link-to-post/