http://wordpress.org/plugins/buckets/

"Now you can make a reusable piece of content. Place it right in the middle of another content area. Or even inside another bucket. Additionally you can use the Advanced Custom Fields plugin to create your own sidebars and add new fields to really customize your Buckets.

You can even create a fully modular site using sidebar areas and just throwing buckets in everywhere!

This plugin is made for developers who like to make their client's lives easier (and in turn, their own)."