I use Friendly for Facebook only because its better than the alternative of using a browser on my iPad. The owners of FB need to just release one of their own that addresses all its readers' needs.
Speaking of which for Twitter I use the Official Twitter app released by Twitter, Inc. They know their users well and their app supplies everything that they require for a good experience.
The Dishfinders app is a social networking platform for food lovers. You can share your dining experiences, post photos and comment on others photos / dish reviews. It's very good on the iPad
Flipboard is a great alternative way to browse through your Facebook and Twitter feeds - turns them into a magazine format. Doesn't replace the standard app browsers, but a lot of fun.