Choose your tools depending on what kind of data you want to show.

I'm currently working on a network map with a few thousand nodes and chose to implement it using a combination of HTML, SVG (Scalable Vector Graphics) and Javascript. CSS takes care of visual feedback such as highlighting focused objects, AJAX sends updates back and forth between server and clients, presenting content such as context menus, site/host details and performance graphs.

Everything is based on W3C standards so it works with all GUI browsers except the Microsoft one.