Call me a square, but I think it looks fine just how it is. I really like things stock, the most modifying I feel comfortable doing to my cars is a pine-tree air freshener on the rearview mirror

I suppose a steering wheel cover or floor mats would be ok as well (I know that's not exactly what you're talking about but it came to mind). I had both in my '87 Honda, they had The Simpsons one them. Maybe you can find some that have a theme you like, such as a TV show, movie, or character(s).

But that's just me, do what you'd like