WordPress Plugin Repository has a brand new widget plugin using it you can add +1 URL, Share Page and Add To Circle options on your site’s widget area. There are many Google Plus widgets available and I only used a few so I cannot say which one is best. I checked this plugin and it works better than others. It loads faster and allows you to change the width of Add To Circle Box so you may give it a try if you like having all three G+ options at the same place.
Simply install and activate it. Then add its widget to your site’s widget area from Appearance -> Widgets Page. Following Screenshot show the widget options: