Adam Erstelle

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

WP Scheduled Styles

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

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 Styles vs Hebcal Shabbat Times