su.pr is part of Stumbleupon and allows posting in advance to Twitter, Facebook, and to Stumble itself.
It has a useful feature that after a few days will tell you the best time to post,which is usually late afternoon or so. I’m getting increased hits using it.
Another bonus: The post doesn’t have to be live on the site when you post it in advance on su.pr, it just has to post on su.pr after the post is published on the blog.
It also does url shortening and will create a custom short url for your site.