Wordpress Sidebar Widget: Addon for Theme Switcher Plugin

1.Theme Switch and Preview : Download

Allows admins or all visitors to switch the blog theme. Has a restricted preview mode for your clients and includes a widget.

2.Theme Switcher : Download

Allow users to switch which theme they use on your WordPress, WordPress MU, or BuddyPress site. Includes a widget for easily putting the theme-switcher as a list or dropdown in your sidebar.