Mashable happens to be one of the most popular websites around these days. You can find all kinds of amazing stories on the site. Many folks are impressed with the social sharing buttons used on that site. I am not a fan of imitating what other sites are doing, but if you want to add mashable-like social media buttons to your site, you should give these plugins a look:
Social Buzz: this plugin adds a shares graph to each post in addition to social media buttons. It has 3 built-in styles and a responsive CSS.
Mashshare: a freemium plugin that adds attractive share buttons to your website. It shows the total share count on each post. You can enhance its capabilities with premium add-ons.
Should you use these plugins? That is up to you. As you can see here, we use regular share buttons to keep things as simple as possible.