I have set the blog to be a different page other than the home page.
I want to have a link from single.php to this blog page.
Is there any function that pulls out URL for the blog ?
To build on Sagive's answer, you'll want to wrap the ID in get_permalink() to get the actual link.
you can use get_option of "page_for_posts" to get the page ID
For additional information of the defualt get_option visit: Option Reference
Hope This Helps.