wpshower: A collection of free wp themes.
Tubepress: A wordpress plugin to add Youtube/Vimeo playlists, etc. to your posts/pages
Timeline: Creating an interactive timeline of your posts: demo at test blog
Google Map Plugin: To create a customized map in your site: demo at test blog
More themes (Thanks to Shannon, refer to the comment below for more…)
Please comment on the post if you know interesting resources.
Graph Paper Press offers themes (including a few free ones) that are very “exhibition friendly.” I’ve also used a couple free WPShower themes. Plus, Smashing Magazine commonly features interesting WP themes and occasionally publishes lists of their favorite free themes.