After having setup more than 3 dozen WordPress sites, I know very well what a pain it can be to go through and populate the site with test data. You have to go in and manually create 5-10 posts, several pages, perhaps some portfolio items in a custom post types, and more. It takes forever.
Well, forget about doing that. The Duplicate Posts Plugin by lopo is one of the single great plugins I have ever used. Not because it provides a huge array of functionality, or dozens and dozens of features, but because it does one thing, and does it very, very well.
The plugin is designed to give you a really easy way to duplicate an already-written post and copy it over to a new post. So, instead of writing 5-10 posts by hand, you write one, then duplicate it 5-10 times.
Not only does the plugin copy over post content, it also does tags, categories, custom fields, featured images, everything.
I have not setup a single WordPress site since I discovered this plugin without installing it.