Google+, Facebook, and Twitter are highly popular these days. Millions of people are active in those sites. Integrating those services into your WordPress site can help you build a more solid community around it. You can get started with Google+, Facebook, and Twitter integration by letting your visitors log on to your WordPress site using their credentials on those sites. Here are 4 plugins that let you do just that:
WP Google Plus Connect: lets your visitors register or log on to your website using their Google+ login credentials.
Simple Facebook Connect: it fully integrates Facebook into WordPress. Lets your visitors log on to your website or leave comments on it using their accounts. It includes Facebook’s social plugins as well.
Simple Twitter Connect: makes it possible your visitors to log in on your website using their Twitter account. Commenting can be done the same way. It offers @anywhere support.
WP Facebook Connect: a simple plugin that brings the power of Facebook to your WordPress site. It uses the Facebook API to create WordPress user accounts.
There are plenty of other Twitter and Facebook connect plugins you can pick up to integrate those services into your site. But the above plugins are simple to use and more than capable of getting the job done.