On my site I have added popups with helpful information and html blocks with small things. Html blocks really give your site some flavor and no one wants to go to a nuked site with the standard blocks available. I have even incorporated a little of my small amount of php knowledge into some blocks such as featured webcam. Since alot of my traffic centers around my webcam portal I made a block that simply includes a featuredcam.php file. it has three variables set for the featured cam and can be easily changed. It either shows the block information with the picture or when you click on the picture it pops up a window with the full sized picture and a link to their site and a close button. When I get better with php and postnuke, I am going to actually release this as a block with some admin features.
The next big addition to my site is a right click navigation menu. Not only does this nonchalantly deter users from getting pictures and source, but it makes the site a little easier to navigate. I put all the code in one file and included it in my theme.php file so that it is accessible from every page on the site. If you would like the code pm me here or on my site and I will gladly send it to you. You can see my site with the link below.