AttachmentsWith this plugin, you can attach multiple files to your posts. This is useful, if you don't want to create a custom post type just for this.
Breadcrumb NavXTIf you need to use a breadcrumb, this is really easy to use and integrate in your PHP code.
Comprehensive Google Map Plugin
This plugin creates a shortcode to embed in your posts/pages and only that. It doesn't appear on the post editing page, stays right out of your way.
Contact Form 7
This is a simple to use contact form that can be used for almost anything. It is very customizable and easy to work with.
Custom Content Type Manager
With this plugin you can easily create custom input fields and assign them to your current post types - or create new ones. This really solved a lot of problems for me.
HTML Page Sitemap
This adds a shortcode to easily add a sitemap to anywhere on your site.
To tell the truth, I don't like the admin GUI logic here, but I didn't find a better gallery plugin yet.