Here are a few scripts I often use, so wanted to keep them accessible in a nice, clean and friendly format.

Drop down menu...

http://javascript-array.com/scripts/simple_drop_down_menu

Lightbox effect (With unlimited content inside) ...

http://fancybox.net

Simple Carousel with lef/right buttons ...

http://www.dynamicdrive.com/dynamicindex4/stepcarousel.htm

Simple Slideshow (Fading in and out) ...

http://jonraasch.com/blog/a-simple-jquery-slideshow

Amazing Gallery (thumbnails, preloading etc) ...

http://galleria.aino.se/

Image mouseover/hover script...

http://www.elated.com/articles/css-rollover-buttons/

Free Flash Video player...

http://www.osmf.org/configurator/fmp/#

Vertical Accordion ...

http://www.sohtanaka.com/web-design/simple-accordion-w-css-and-jquery/

Email + Validation ...

http://www.raymondselda.com/php-contact-form-with-jquery-validation/

Scroll bar customization ...

http://www.hesido.com/web.php?page=customscrollbar

Clean and simple Image Gallery ...

http://www.dynamicdrive.com/dynamicindex4/thumbnail2.htm

Tabbed divs ...

http://www.sohtanaka.com/web-design/simple-tabs-w-css-jquery/

Carousel with buttons and rollover text ...

http://www.dreamcss.com/2009/04/create-beautiful-jquery-sliders.html

Pure JS and CSS popup ...

http://yensdesign.com/tutorials/popupjquery/