K2 Tabs is one of the best K2 add-ons, which comes with pre-built 25 tab themes and styles. It can automatically pull your K2 contents, with a click on one button.
K2 Accordion is one of the best K2 add-ons, which comes with pre-built 25 Accordion themes and styles.
3D Slicebox is one of the most modern revolutionary image slideshow modules, which kills the flash based 3D slideshows from its core.
Color Accordion is a nice and fully configurable Accordion Module, which supports Joomla Contents, K2 Contents and Joomla Modules as well.
HTML5 Video Gallery is a great module to showcase your videos in a nice sliding manner. All you need to do is, define the video URLs, thumbnail URL and title.