Here is a list of four websites that allows auto publishing of RSS/Atom feeds to various social networking websites like Facebook, Twitter, LinkedIN and more.
TwitterFeed
Automatically posts one or many RSS feeds to Facebook, Twitter and LinkedIN. You can add many social accounts posting a number of RSS feeds and its completely free of cost. Read its step by step guide on its usage and features.
DlvrIT
Another online service allows you to auto share blog or any other RSS feed to popular social networks, also provides stats and widgets showing number or clicks and followers to use on your site. Widgets are highly customizable. Comes in both free and premium offers, read its usage guide here.
HootSuite
Famous service comes in 30 days free trial and then you have to upgrade it to Pro. Using this service you can easily manage unlimited social networking accounts and profiles from one interface. You can schedule Facebook, Google + Pages, LinkedIn posts and Twitter messages. Provides Integrated social analytics.
Seesmic
Using Seesmic you can Post to Twitter, Facebook, Linkedin, Tumblr (more are coming as said on its site), you can post from many social accounts, you can schedule your posts, select Thumbnails for the attached links, you can post from iPhone, iPad and Android, you can create and post a Groups of accounts and more using this free service.