I've been toying around with different ways to integrate WordPress and Omeka for our site at http://www.ohiocivilwar150.org/ and just thought I would share one handy approach for doing so. Aside from creating matching themes for each platform, this seems like it might be a next step for some projects.
In WordPress, you need two plugins (or possibly 3 - see below):
Featured Content Showcase
Page Links To
Featured Content Showcase (FCS) adds a slideshow to your WordPress theme that you can use to easily feature posts using the WP post thumbnail feature (version 2.9+). Page Links To (PLT) adds the ability to override the URL of a post or page so that it redirects somewhere else (e.g. to an Omeka Exhibit).
Just create a "dummy" post with a thumbnail image, a title and brief description, mark it featured according to the FCS instructions and redirect the post to your exhibit using the PLT instructions. Pretty easy.
If you don't want the dummy posts to appear in your main blog feed or other areas of your site, you can use the Category Visibility plugin (http://wordpress.org/extend/plugins/category-visibility-ipeat/).