Easy Custom Auto Excerpt is a WordPress plugin to cut/excerpt your post displayed on the home, search or archive pages. By using this plugin you don’t need to excerpt your post manualy; just activate the plugin, configure the word length and you’re good to go.. You can also change the image thumbnail position for the generated excerpt.
The important thing to notice is, make sure your theme is compitable with ECAE. Some themes, especially genesis based, has its own excerpt function, and sometimes cannot work properly with ECAE. You can always download the free version first at wordpress.org, before deciding to buy.