Adding visual interest to a website without cluttering it or making the visuals detract from the content

In working on a redesigned website for my university program I feel like I've got a pretty solid foundation. The purpose of the website is to be both informational but, also, to be "fun" and "inviting." So, we have used some Google Web Fonts for typography and we've done some work with headings, line hight, and line length. Now, we would like to add some visual elements to make the pages more attractive but that don't detract from the content. What are some effective methods for adding visual interest? One suggestion was a "water mark" type image but I have issues with that because it could cause problems with older browsers.