How should I organize all this material?

Soon after I started using declicious to bookmark primary source sites, I knew I had a problem. How could I best organize these bookmarks to make them easy for students to navigate? I still haven't come up with a satisfactory answer. To the left, you'll see the tag cloud for my bookmarks. Below the cloud, you'll find a list of my bookmarks and links to my delcious site. I'm toying with the idea of organizing my bookmarks by time period. However, the students I work with focus on a wide array of topics and time periods, so I'm not sure organization by time period will work. Suggestions?