mabujo

googleCards is a google+ wordpress plugin. 
It adds a widget to your blog that will display a link to your google+ profile so people can add you to a circle (follow you). It also displays your name, profile picture and the number of people who have you in circles.
The plugin uses caching to store your google plus profile data to eliminate checking google+ on every page load. 
For the caching to work, your web-server needs to be able to write to wp-content. (a lot of plugins require this so it should be fine). 
If the plugin cannot cache it will still work, but will store the data in the database instead. If caching is working you should see a file called plus_card.txt in /wp-content/cache/. 
As of version 0.4, caching will also failback to using transients to store your scraped google plus data.
Plugin page : <a href="http://plusdevs.com/google-wordpress-plugin/" rel="nofollow ugc">Google plus wordpress plugin @ plusdevs</a>

googleCards

A simple plugin that adds a google+ widget for linking to your google+ profile and showing your number of followers

hrosenhagen

Hocus Pocus Buttons is a WordPress-Plugin that provides sidebar widget with a widerange set of buttons for social bookmarking websites. However each button is only visible to the user if he has visited the corresponding site lately.
The goal is not to disturb the user by using too many buttons / links (since he could probably only use one or two at all) and rather only show relevant services.
<h3>More</h3>
For information about the use of this plugin visit the <a href="http://www.interessante-zeiten.de/goodies/hocus-pocus-buttons-wordpress-plugin" rel="nofollow ugc">plugin page</a>

Hocus Pocus Buttons

Automagically show or don't show buttons/links for social bookmarking sites, depending on the sites the user has visited lately.

googleCards vs Hocus Pocus Buttons