http://brm.io/jekyll-post-links/
I modified the original post_url source to generate a complete anchor tag with the url and title all pulled from the post. You can optionally change the link text too. I prefer this to manually typing post links since this helps keep them up to date during development, even if you change permalinks, and the compiler will warn if you accidentally a broken link.
Drop the jekyll-post-link.rb file in your _plugins directory and you're good to go.
Usage of post_link is as follows:
{% post_link post text %}
Where post is a post in the usual date-slug format.
Optional: if specified text is the anchor text, otherwise it's the post title