Theme Switcher Reloaded is an updated and much improved version of the original Theme Switcher. Comes with a widget and can also switch themes via URL
Allow users to preview and/or download/buy themes on the front end
WordPress Theme Demo Bar allows any wordpress theme to be previewed without activating it. A demo bar would be shown on top of page, allow users to pr
The Preview Themes plugin allows wordpress users to preview all installed themes without having to activate and deactivate them simultaneously.
Allows admins or all visitors to switch the blog theme. Has a restricted preview mode for your clients and includes a widget.
WP Theme Showcase ext and i18n displays themes and info from their style.css with one or two indices. Lots of features and options and a widget.
WP Theme plugin allow you to preview a theme without activating it from admin panel.
Allows you test how a theme looks on your site without activating it.
Disables the cool but sometimes annoying theme preview feature added in WordPress 2.6.