Since emails don’t have a very long lifespan (they’re usually read and then deleted), you can be more trendy than you might otherwise be with design. You still want to stay true to your brand or overall campaign look, of course, but you can dip into trends for some added fun.
For instance, animated GIF images have become very popular in emails lately. What was once a tacky 90s art form is now a trend being used in email because nearly all email clients support gif files.
Another up-and-coming idea is to put video in email. Not all email clients support videos in email, but as long as you include a good fallback image (perhaps an animated GIF of your video) and supporting text, why not have the benefit for those subscribers whose email clients do support it.