Adam Erstelle

This plugin allows a wordpress administrator to schedule a different theme to display on the website for holidays or special events for all visitors.
The theme will be overridden on the live site for all people who visit the site. Great for setting a Christmas theme!
If you just want to have a css file added instead of a whole theme, check out the wp-scheduled-styles plugin.

WP Scheduled Themes

Schedule a theme to display on the live site for holidays or special events. (Available from Appearance - Scheduled Themes)

mradwin

Displays Shabbat candle lighting times for a USA zip code in a 
widget. Candle lighting time information comes from Hebcal.com.
Hebcal.com is a free Jewish calendar and holiday web site. It includes 
a powerful custom Jewish calendar form that lets you generate a list 
of Jewish holidays for any year (past, present or future). Also 
available is a Hebrew date converter, Shabbat candle lighting times 
and Torah readings, and a page to look up yahrzeits, birthdays and 
anniversaries.

Hebcal Shabbat Times

Displays Shabbat candle lighting times for a USA zip code in a widget.

WP Scheduled Themes vs Hebcal Shabbat Times