We respond well to small delighters.
Can you create some small and unexpected pleasurable things to delight your visitors? It can be a small game, a video or maybe you can trigger the gatherer in your visitors and let the collect points or badges or other stuff on your website. Don't go overboard though, it's all about the small things. You don't want to distract people from actually buying stuff on your website.
An example of a fun delighter in the Mailchimp interface: