I have been interested (obsessed, actually) with the idea of navigating and interacting with 3D worlds on the Web since the early days of VRML. Navigating and interacting with 3D on the internet has a long, torturous history. The solutions have fallen basically into two camps, both with their strong points and downsides. First, desktop gaming (such as Half Life, World of Warcraft, etc.) and virtual worlds (such as Secondlife) have been hugely successful at connecting users into a massive consensual hallucination. The downside of course, is that the entry points are still closed systems such as Windows, Mac and/or game consoles. The second, and less successful camp, is browser-based 3D. Almost as soon as the Web came into being, 3D was touted as the "next big thing." VRML, Java, and eventually Flash have all been used in a multitude of combinations to deliver interactive 3D to users on the web. Although these worlds were in-browser, they were (for the most part) solitary experiences and also required an additional plug-in.
If you are running one of the newer browsers, check out some of these sample works particularly relevant to BIM. Note: You will need to enable WebGL in your browser.
Fractal Lab, C'mon, its fractals that you can explore in 3D. Pretty damn cool.
PhiloGL allows you to explore parametric geometry equations.
Tessellations! Exporting to an OBJ file is a nice touch.
Thingiverse.com is an online community where makers share their 3D creations. Any entry that has an STL file will have a little gray cube icon. Click and you get a 3D preview - with no plugins!
3DTin is a Lego style modeler. You build 3D models by placing colored blocks. It is quite primitive (literally), but demonstrates a good start towards interactive 3D modeling on the web.